v3.26.1
Shareholder Report
 12 Months Ended
Apr. 30, 2026
USD ($)
$ / shares
Shareholder Report [Line Items]  
Document Type N-CSR
Amendment Flag false
Registrant Name Franklin Federal Tax-Free Income Fund
Entity Central Index Key 0000357310
Entity Investment Company Type N-1A
Document Period End Date Apr. 30, 2026
Shareholder Report Annual or Semi-Annual annual shareholder report
Class A  
Shareholder Report [Line Items]  
Fund Name Franklin Federal Tax-Free Income Fund
Class Name Class A
Trading Symbol FFQAX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about Franklin Federal Tax-Free Income Fund for the period May 1, 2025, to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.
Material Fund Change Notice [Text Block]
This report describes changes to the Fund that occurred during the reporting period.
Additional Information Phone Number (800) DIAL BEN/342-5236
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (based on a hypothetical $10,000 investment)
Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Class A
$80
0.78%
Expenses Paid, Amount $ 80
Expense Ratio, Percent 0.78%
Factors Affecting Performance [Text Block]
HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?
For the twelve months ended April 30, 2026, Class A shares of Franklin Federal Tax-Free Income Fund returned 6.24%. The Fund compares its performance to the  Bloomberg Municipal Bond Index, which returned 6.34% for the same period.
PERFORMANCE HIGHLIGHTS
Top contributors to performance:
An overweight allocation to:
↑
Bonds with no external credit rating
↑
Bonds with 20 years or more to maturity
↑
BBB rated bonds
Top detractors from performance:
↓
Underweight to bonds with 10 years or less to maturity
↓
Selection in A rated bonds
↓
Selection in AAA rated bonds
Performance Past Does Not Indicate Future [Text] The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future.
Line Graph [Table Text Block]
image
Average Annual Return [Table Text Block]
AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended April 30, 2026
 
1 Year
5 Year
10 Year
Class A
6.24
0.59
1.85
Class A (with sales charge)
2.25
-0.17
1.46
Bloomberg Municipal Bond Index
6.34
0.90
2.20
No Deduction of Taxes [Text Block] The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.
Material Change Date May 01, 2025
Updated Performance Information Location [Text Block]
For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.
Important data provider notices and terms available at www.franklintempletondatasources.com.
Net Assets $ 7,755,931,120
Holdings Count | $ / shares 979
Advisory Fees Paid, Amount $ 35,589,401
Investment Company Portfolio Turnover 9.99%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of April 30, 2026)
Total Net Assets
$7,755,931,120
Total Number of Portfolio Holdings
979
Total Management Fee Paid
$35,589,401
Portfolio Turnover Rate
9.99%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of April 30, 2026)
Portfolio Composition*  (% of Total Investments)
image
 [1]
Material Fund Change [Text Block]
HOW HAS THE FUND CHANGED?
Effective May 30, 2025, Paul M. Drury stepped down as portfolio manager of the Fund.
This is a summary of a certain change to the Fund since May 1, 2025. For more complete information, you may review the Fund’s current prospectus and any applicable supplements and the Fund’s next prospectus, which we expect to be available by September 1, 2026, at https://www.franklintempleton.com/regulatory-fund-documents or upon request at (800) DIAL BEN/342-5236 or prospectus.us.franklintempleton@fisglobal.com.
Summary of Change Legend [Text Block] This is a summary of a certain change to the Fund since May 1, 2025. For more complete information, you may review the Fund’s current prospectus and any applicable supplements and the Fund’s next prospectus, which we expect to be available by September 1, 2026, at https://www.franklintempleton.com/regulatory-fund-documents or upon request at (800) DIAL BEN/342-5236 or prospectus.us.franklintempleton@fisglobal.com.
Updated Prospectus Phone Number (800) DIAL BEN/342-5236
Updated Prospectus Email Address prospectus.us.franklintempleton@fisglobal.com
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class A1  
Shareholder Report [Line Items]  
Fund Name Franklin Federal Tax-Free Income Fund
Class Name Class A1
Trading Symbol FKTIX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about Franklin Federal Tax-Free Income Fund for the period May 1, 2025, to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.
Material Fund Change Notice [Text Block]
This report describes changes to the Fund that occurred during the reporting period.
Additional Information Phone Number (800) DIAL BEN/342-5236
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (based on a hypothetical $10,000 investment)
Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Class A1
$65
0.63%
Expenses Paid, Amount $ 65
Expense Ratio, Percent 0.63%
Factors Affecting Performance [Text Block]
HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?
For the twelve months ended April 30, 2026, Class A1 shares of Franklin Federal Tax-Free Income Fund returned 6.39%. The Fund compares its performance to the  Bloomberg Municipal Bond Index, which returned 6.34% for the same period.
PERFORMANCE HIGHLIGHTS
Top contributors to performance:
An overweight allocation to:
↑
Bonds with no external credit rating
↑
Bonds with 20 years or more to maturity
↑
BBB rated bonds
Top detractors from performance:
↓
Underweight to bonds with 10 years or less to maturity
↓
Selection in A rated bonds
↓
Selection in AAA rated bonds
Performance Past Does Not Indicate Future [Text] The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future.
Line Graph [Table Text Block]
image
Average Annual Return [Table Text Block]
AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended April 30, 2026
 
1 Year
5 Year
10 Year
Class A1
6.39
0.74
1.97
Class A1 (with sales charge)
2.40
-0.03
1.58
Bloomberg Municipal Bond Index
6.34
0.90
2.20
No Deduction of Taxes [Text Block] The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.
Material Change Date May 01, 2025
Updated Performance Information Location [Text Block]
For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.
Important data provider notices and terms available at www.franklintempletondatasources.com.
Net Assets $ 7,755,931,120
Holdings Count | $ / shares 979
Advisory Fees Paid, Amount $ 35,589,401
Investment Company Portfolio Turnover 9.99%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of April 30, 2026)
Total Net Assets
$7,755,931,120
Total Number of Portfolio Holdings
979
Total Management Fee Paid
$35,589,401
Portfolio Turnover Rate
9.99%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of April 30, 2026)
Portfolio Composition*  (% of Total Investments)
image
 [2]
Material Fund Change [Text Block]
HOW HAS THE FUND CHANGED?
Effective May 30, 2025, Paul M. Drury stepped down as portfolio manager of the Fund.
This is a summary of a certain change to the Fund since May 1, 2025. For more complete information, you may review the Fund’s current prospectus and any applicable supplements and the Fund’s next prospectus, which we expect to be available by September 1, 2026, at https://www.franklintempleton.com/regulatory-fund-documents or upon request at (800) DIAL BEN/342-5236 or prospectus.us.franklintempleton@fisglobal.com.
Summary of Change Legend [Text Block] This is a summary of a certain change to the Fund since May 1, 2025. For more complete information, you may review the Fund’s current prospectus and any applicable supplements and the Fund’s next prospectus, which we expect to be available by September 1, 2026, at https://www.franklintempleton.com/regulatory-fund-documents or upon request at (800) DIAL BEN/342-5236 or prospectus.us.franklintempleton@fisglobal.com.
Updated Prospectus Phone Number (800) DIAL BEN/342-5236
Updated Prospectus Email Address prospectus.us.franklintempleton@fisglobal.com
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class C  
Shareholder Report [Line Items]  
Fund Name Franklin Federal Tax-Free Income Fund
Class Name Class C
Trading Symbol FRFTX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about Franklin Federal Tax-Free Income Fund for the period May 1, 2025, to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.
Material Fund Change Notice [Text Block]
This report describes changes to the Fund that occurred during the reporting period.
Additional Information Phone Number (800) DIAL BEN/342-5236
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (based on a hypothetical $10,000 investment)
Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Class C
$121
1.18%
Expenses Paid, Amount $ 121
Expense Ratio, Percent 1.18%
Factors Affecting Performance [Text Block]
HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?
For the twelve months ended April 30, 2026, Class C shares of Franklin Federal Tax-Free Income Fund returned 5.82%. The Fund compares its performance to the  Bloomberg Municipal Bond Index, which returned 6.34% for the same period.
PERFORMANCE HIGHLIGHTS
Top contributors to performance:
An overweight allocation to:
↑
Bonds with no external credit rating
↑
Bonds with 20 years or more to maturity
↑
BBB rated bonds
Top detractors from performance:
↓
Underweight to bonds with 10 years or less to maturity
↓
Selection in A rated bonds
↓
Selection in AAA rated bonds
Performance Past Does Not Indicate Future [Text] The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future.
Line Graph [Table Text Block]
image
Average Annual Return [Table Text Block]
AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended April 30, 2026
 
1 Year
5 Year
10 Year
Class C
5.82
0.19
1.41
Class C (with sales charge)
4.82
0.19
1.41
Bloomberg Municipal Bond Index
6.34
0.90
2.20
No Deduction of Taxes [Text Block] The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.
Material Change Date May 01, 2025
Updated Performance Information Location [Text Block]
For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.
Important data provider notices and terms available at www.franklintempletondatasources.com.
Net Assets $ 7,755,931,120
Holdings Count | $ / shares 979
Advisory Fees Paid, Amount $ 35,589,401
Investment Company Portfolio Turnover 9.99%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of April 30, 2026)
Total Net Assets
$7,755,931,120
Total Number of Portfolio Holdings
979
Total Management Fee Paid
$35,589,401
Portfolio Turnover Rate
9.99%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of April 30, 2026)
Portfolio Composition*  (% of Total Investments)
image
 [3]
Material Fund Change [Text Block]
HOW HAS THE FUND CHANGED?
Effective May 30, 2025, Paul M. Drury stepped down as portfolio manager of the Fund.
This is a summary of a certain change to the Fund since May 1, 2025. For more complete information, you may review the Fund’s current prospectus and any applicable supplements and the Fund’s next prospectus, which we expect to be available by September 1, 2026, at https://www.franklintempleton.com/regulatory-fund-documents or upon request at (800) DIAL BEN/342-5236 or prospectus.us.franklintempleton@fisglobal.com.
Summary of Change Legend [Text Block] This is a summary of a certain change to the Fund since May 1, 2025. For more complete information, you may review the Fund’s current prospectus and any applicable supplements and the Fund’s next prospectus, which we expect to be available by September 1, 2026, at https://www.franklintempleton.com/regulatory-fund-documents or upon request at (800) DIAL BEN/342-5236 or prospectus.us.franklintempleton@fisglobal.com.
Updated Prospectus Phone Number (800) DIAL BEN/342-5236
Updated Prospectus Email Address prospectus.us.franklintempleton@fisglobal.com
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class R6  
Shareholder Report [Line Items]  
Fund Name Franklin Federal Tax-Free Income Fund
Class Name Class R6
Trading Symbol FFTQX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about Franklin Federal Tax-Free Income Fund for the period May 1, 2025, to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.
Material Fund Change Notice [Text Block]
This report describes changes to the Fund that occurred during the reporting period.
Additional Information Phone Number (800) DIAL BEN/342-5236
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (based on a hypothetical $10,000 investment)
Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Class R6
$50
0.48%
Expenses Paid, Amount $ 50
Expense Ratio, Percent 0.48%
Factors Affecting Performance [Text Block]
HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?
For the twelve months ended April 30, 2026, Class R6 shares of Franklin Federal Tax-Free Income Fund returned 6.55%. The Fund compares its performance to the  Bloomberg Municipal Bond Index, which returned 6.34% for the same period.
PERFORMANCE HIGHLIGHTS
Top contributors to performance:
An overweight allocation to:
↑
Bonds with no external credit rating
↑
Bonds with 20 years or more to maturity
↑
BBB rated bonds
Top detractors from performance:
↓
Underweight to bonds with 10 years or less to maturity
↓
Selection in A rated bonds
↓
Selection in AAA rated bonds
Performance Past Does Not Indicate Future [Text] The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future.
Line Graph [Table Text Block]
image
Average Annual Return [Table Text Block]
AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended April 30, 2026
 
1 Year
5 Year
10 Year
Class R6
6.55
0.89
2.07
Bloomberg Municipal Bond Index
6.34
0.90
2.20
No Deduction of Taxes [Text Block] The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.
Material Change Date May 01, 2025
Updated Performance Information Location [Text Block]
For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.
Important data provider notices and terms available at www.franklintempletondatasources.com.
Net Assets $ 7,755,931,120
Holdings Count | $ / shares 979
Advisory Fees Paid, Amount $ 35,589,401
Investment Company Portfolio Turnover 9.99%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of April 30, 2026)
Total Net Assets
$7,755,931,120
Total Number of Portfolio Holdings
979
Total Management Fee Paid
$35,589,401
Portfolio Turnover Rate
9.99%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of April 30, 2026)
Portfolio Composition*  (% of Total Investments)
image
 [4]
Material Fund Change [Text Block]
HOW HAS THE FUND CHANGED?
Effective May 30, 2025, Paul M. Drury stepped down as portfolio manager of the Fund.
This is a summary of a certain change to the Fund since May 1, 2025. For more complete information, you may review the Fund’s current prospectus and any applicable supplements and the Fund’s next prospectus, which we expect to be available by September 1, 2026, at https://www.franklintempleton.com/regulatory-fund-documents or upon request at (800) DIAL BEN/342-5236 or prospectus.us.franklintempleton@fisglobal.com.
Summary of Change Legend [Text Block] This is a summary of a certain change to the Fund since May 1, 2025. For more complete information, you may review the Fund’s current prospectus and any applicable supplements and the Fund’s next prospectus, which we expect to be available by September 1, 2026, at https://www.franklintempleton.com/regulatory-fund-documents or upon request at (800) DIAL BEN/342-5236 or prospectus.us.franklintempleton@fisglobal.com.
Updated Prospectus Phone Number (800) DIAL BEN/342-5236
Updated Prospectus Email Address prospectus.us.franklintempleton@fisglobal.com
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Advisor Class  
Shareholder Report [Line Items]  
Fund Name Franklin Federal Tax-Free Income Fund
Class Name Advisor Class
Trading Symbol FAFTX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about Franklin Federal Tax-Free Income Fund for the period May 1, 2025, to April 30, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at (800) DIAL BEN/342-5236.
Material Fund Change Notice [Text Block]
This report describes changes to the Fund that occurred during the reporting period.
Additional Information Phone Number (800) DIAL BEN/342-5236
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST YEAR? (based on a hypothetical $10,000 investment)
Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Advisor Class
$55
0.53%
Expenses Paid, Amount $ 55
Expense Ratio, Percent 0.53%
Factors Affecting Performance [Text Block]
HOW DID THE FUND PERFORM LAST YEAR AND WHAT AFFECTED ITS PERFORMANCE?
For the twelve months ended April 30, 2026, Advisor Class shares of Franklin Federal Tax-Free Income Fund returned 6.59%. The Fund compares its performance to the  Bloomberg Municipal Bond Index, which returned 6.34% for the same period.
PERFORMANCE HIGHLIGHTS
Top contributors to performance:
An overweight allocation to:
↑
Bonds with no external credit rating
↑
Bonds with 20 years or more to maturity
↑
BBB rated bonds
Top detractors from performance:
↓
Underweight to bonds with 10 years or less to maturity
↓
Selection in A rated bonds
↓
Selection in AAA rated bonds
Performance Past Does Not Indicate Future [Text] The Fund’s past performance is not necessarily an indication of how the Fund will perform in the future.
Line Graph [Table Text Block]
image
Average Annual Return [Table Text Block]
AVERAGE ANNUAL TOTAL RETURNS (%) Period Ended April 30, 2026
 
1 Year
5 Year
10 Year
Advisor Class
6.59
0.86
2.08
Bloomberg Municipal Bond Index
6.34
0.90
2.20
No Deduction of Taxes [Text Block] The graph and table do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or redemption of Fund shares.
Material Change Date May 01, 2025
Updated Performance Information Location [Text Block]
For current month-end performance, please call Franklin Templeton at (800) DIAL BEN/342-5236 or visit
https://www.franklintempleton.com/investments/options/mutual-funds.
Important data provider notices and terms available at www.franklintempletondatasources.com.
Net Assets $ 7,755,931,120
Holdings Count | $ / shares 979
Advisory Fees Paid, Amount $ 35,589,401
Investment Company Portfolio Turnover 9.99%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of April 30, 2026)
Total Net Assets
$7,755,931,120
Total Number of Portfolio Holdings
979
Total Management Fee Paid
$35,589,401
Portfolio Turnover Rate
9.99%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of April 30, 2026)
Portfolio Composition*  (% of Total Investments)
image
 [5]
Material Fund Change [Text Block]
HOW HAS THE FUND CHANGED?
Effective May 30, 2025, Paul M. Drury stepped down as portfolio manager of the Fund.
This is a summary of a certain change to the Fund since May 1, 2025. For more complete information, you may review the Fund’s current prospectus and any applicable supplements and the Fund’s next prospectus, which we expect to be available by September 1, 2026, at https://www.franklintempleton.com/regulatory-fund-documents or upon request at (800) DIAL BEN/342-5236 or prospectus.us.franklintempleton@fisglobal.com.
Summary of Change Legend [Text Block] This is a summary of a certain change to the Fund since May 1, 2025. For more complete information, you may review the Fund’s current prospectus and any applicable supplements and the Fund’s next prospectus, which we expect to be available by September 1, 2026, at https://www.franklintempleton.com/regulatory-fund-documents or upon request at (800) DIAL BEN/342-5236 or prospectus.us.franklintempleton@fisglobal.com.
Updated Prospectus Phone Number (800) DIAL BEN/342-5236
Updated Prospectus Email Address prospectus.us.franklintempleton@fisglobal.com
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
[1]
* Does not include derivatives, except purchased options, if any.  
[2]
* Does not include derivatives, except purchased options, if any.  
[3]
* Does not include derivatives, except purchased options, if any.  
[4]
* Does not include derivatives, except purchased options, if any.  
[5]
* Does not include derivatives, except purchased options, if any.