Share Class

AVERAGE ANNUAL TOTAL RETURNS

YTD 1-YR 3-YR 5-YR 10-YR INCEPTION*
A Shares (THIMX)
Without sales charge3.30%0.77%1.74%2.08%3.73%4.72%
With sales charge1.26%-1.23%1.06%1.67%3.52%4.64%
YTD 1-YR 3-YR 5-YR 10-YR INCEPTION*
C Shares (THMCX)
Without sales charge2.95%0.38%1.39%1.74%3.41%3.90%
With sales charge2.35%-0.22%1.39%1.74%3.41%3.90%
YTD 1-YR 3-YR 5-YR 10-YR INCEPTION*
I Shares (THMIX)3.48%1.00%2.05%2.39%4.04%4.43%
YTD 1-YR 3-YR 5-YR 10-YR INCEPTION*
A Shares (THIMX)
Without sales charge3.26%-0.08%1.91%2.13%3.74%4.73%
With sales charge1.23%-2.11%1.23%1.72%3.53%4.65%
YTD 1-YR 3-YR 5-YR 10-YR INCEPTION*
C Shares (THMCX)
Without sales charge3.01%-0.40%1.58%1.80%3.44%3.91%
With sales charge2.41%-0.98%1.58%1.80%3.44%3.91%
YTD 1-YR 3-YR 5-YR 10-YR INCEPTION*
I Shares (THMIX)3.42%0.15%2.19%2.44%4.06%4.45%

Returns for less than one year are not annualized.
*Inception date for Class A Shares 7/22/1991.

Returns for less than one year are not annualized.
*Inception date for Class C Shares 9/1/1994.

Returns for less than one year are not annualized.
*Inception date for Class I Shares 7/5/1996.

Performance data shown represents past performance and is no guarantee of future results. Investment return and principal value will fluctuate so shares, when redeemed, may be worth more or less than their original cost. Current performance may be lower or higher than quoted.

The maximum sales charge for the Fund's A shares is 2.00%.

C shares include a 0.60% contingent deferred sales charge (CDSC) for the first year only.

There is no up-front sales charge for the I shares.

There is no up-front sales charge for class R shares.

FUND OPERATING EXPENSES — Class A Shares

Gross Annual Operating Expenses (as reported in the most recent Prospectus)0.92%
Actual Annual Operating Expenses (fiscal year to date, as of 9/30/2017)0.92%

Expense Ratios – Expressed as a percentage of total fund assets and include management fees and operating costs. Expense ratios fluctuate over time and the expense ratio in the prospectus may differ from the actual expense ratio. The fund's total return includes the deduction of expenses.

For more detailed information on fund expenses, please see the fund's prospectus.

FUND OPERATING EXPENSES — Class C Shares

Gross Annual Operating Expenses (as reported in the most recent Prospectus)1.27%
Net Annual Operating Expenses (as reported in the most recent Prospectus)1.24%
Actual Annual Operating Expenses (fiscal year to date, as of 9/30/2017)1.24%

Thornburg Investment Management and/or Thornburg Securities Corporation have contractually agreed to waive fees and reimburse expenses through at least April 10, 2018, so that actual expenses do not exceed the net expense ratio above.

Expense Ratios – Expressed as a percentage of total fund assets and include management fees and operating costs. Expense ratios fluctuate over time and the expense ratio in the prospectus may differ from the actual expense ratio. The fund's total return includes the deduction of expenses.

For more detailed information on fund expenses, please see the fund's prospectus.

FUND OPERATING EXPENSES — Class I Shares

Gross Annual Operating Expenses (as reported in the most recent Prospectus)0.61%
Actual Annual Operating Expenses (fiscal year to date, as of 9/30/2017)0.62%

Expense Ratios – Expressed as a percentage of total fund assets and include management fees and operating costs. Expense ratios fluctuate over time and the expense ratio in the prospectus may differ from the actual expense ratio. The fund's total return includes the deduction of expenses.

For more detailed information on fund expenses, please see the fund's prospectus.

MORNINGSTAR RATING

Overall Morningstar Rating among 257 Muni National Intermediate funds, based on risk-adjusted returns for class A shares, using a weighted average of the fund's three-, five- and ten-year ratings: respectively, 2 stars, 2 stars and 3 stars among 257, 224 and 156 funds, as of 10/31/2017.

Additional Rating and Ranking Information

To determine a fund's Morningstar Rating™, funds and other managed products with at least a three-year history are ranked in their categories by their Morningstar Risk-Adjusted Return scores. The top 10% receive 5 stars; the next 22.5%, 4 stars; the middle 35%, 3 stars; the next 22.5%, 2 stars; and the bottom 10% receive 1 star. The Risk-Adjusted Return accounts for variation in a managed product's monthly excess performance (excluding sales charges), placing more emphasis on downward variations and rewarding consistent performance. Other share classes may have different performance characteristics. © 2017 Morningstar, Inc. All Rights Reserved. The information contained herein: (1) is proprietary to Morningstar and/or its content providers; (2) may not be copied or distributed; and (3) is not warranted to be accurate, complete or timely. Neither Morningstar nor its content providers are responsible for any damages or losses arising from any use of this information. Past performance is no guarantee of future results.

MORNINGSTAR RATING

Overall Morningstar Rating among 257 Muni National Intermediate funds, based on risk-adjusted returns for class C shares, using a weighted average of the fund's three-, five- and ten-year ratings: respectively, 1 star, 2 stars and 2 stars among 257, 224 and 156 funds, as of 10/31/2017.

Additional Rating and Ranking Information

To determine a fund's Morningstar Rating™, funds and other managed products with at least a three-year history are ranked in their categories by their Morningstar Risk-Adjusted Return scores. The top 10% receive 5 stars; the next 22.5%, 4 stars; the middle 35%, 3 stars; the next 22.5%, 2 stars; and the bottom 10% receive 1 star. The Risk-Adjusted Return accounts for variation in a managed product's monthly excess performance (excluding sales charges), placing more emphasis on downward variations and rewarding consistent performance. Other share classes may have different performance characteristics. © 2017 Morningstar, Inc. All Rights Reserved. The information contained herein: (1) is proprietary to Morningstar and/or its content providers; (2) may not be copied or distributed; and (3) is not warranted to be accurate, complete or timely. Neither Morningstar nor its content providers are responsible for any damages or losses arising from any use of this information. Past performance is no guarantee of future results.

MORNINGSTAR RATING

Overall Morningstar Rating among 257 Muni National Intermediate funds, based on risk-adjusted returns for class I shares, using a weighted average of the fund's three-, five- and ten-year ratings: respectively, 3 stars, 3 stars and 4 stars among 257, 224 and 156 funds, as of 10/31/2017.

Additional Rating and Ranking Information

To determine a fund's Morningstar Rating™, funds and other managed products with at least a three-year history are ranked in their categories by their Morningstar Risk-Adjusted Return scores. The top 10% receive 5 stars; the next 22.5%, 4 stars; the middle 35%, 3 stars; the next 22.5%, 2 stars; and the bottom 10% receive 1 star. The Risk-Adjusted Return accounts for variation in a managed product's monthly excess performance (excluding sales charges), placing more emphasis on downward variations and rewarding consistent performance. Other share classes may have different performance characteristics. © 2017 Morningstar, Inc. All Rights Reserved. The information contained herein: (1) is proprietary to Morningstar and/or its content providers; (2) may not be copied or distributed; and (3) is not warranted to be accurate, complete or timely. Neither Morningstar nor its content providers are responsible for any damages or losses arising from any use of this information. Past performance is no guarantee of future results.

30-day Yields With Sales Charge as of 10/31/2017 — Class A Shares

Annualized Distribution Yield2.02%
SEC Yield1.14%

30-day Yields With Sales Charge as of 10/31/2017 — Class C Shares

Annualized Distribution Yield1.74%
SEC Yield0.84%
Without the fee waivers and expense reimbursements described above the Annualized Distribution yield would have been 1.72%, and the SEC yield would have been 0.82%.

30-day Yields With Sales Charge as of 10/31/2017 — Class I Shares

Annualized Distribution Yield2.37%
SEC Yield1.47%

Dividends and Capital Gains — Class A Shares

Dividend (paid Oct 31, 2017)$0.02511
Capital Gains (2017)None Paid

Dividends and Capital Gains — Class C Shares

Dividend (paid Oct 31, 2017)$0.02124
Capital Gains (2017)None Paid

Dividends and Capital Gains — Class I Shares

Dividend (paid Oct 31, 2017)$0.02877
Capital Gains (2017)None Paid

Net Asset Value (NAV) History as of 10/31/2017 — Class A Shares

Net Asset Value (NAV) History as of 10/31/2017 — Class C Shares

Net Asset Value (NAV) History as of 10/31/2017 — Class I Shares

Important Information
Before investing, carefully consider the Fund’s investment goals, risks, charges, and expenses. For a prospectus or summary prospectus containing this and other information, contact your financial advisor or visit our literature center. Read them carefully before investing.

Investments carry risks, including possible loss of principal. Portfolios investing in bonds have the same interest rate, inflation, and credit risks that are associated with the underlying bonds. The value of bonds will fluctuate relative to changes in interest rates, decreasing when interest rates rise. Unlike bonds, bond funds have ongoing fees and expenses. Investments in the Fund are not FDIC insured, nor are they bank deposits or guaranteed by a bank or any other entity.

Credit quality ratings for Thornburg’s municipal portfolios used the highest rating available from either S&P Global Ratings or Moody’s Investors Service.

A bond credit rating assesses the financial ability of a debt issuer to make timely payments of principal and interest. Ratings of AAA (the highest), AA, A, and BBB are investment-grade quality. Ratings of BB, B, CCC, CC, C and D (the lowest) are considered below investment grade, speculative grade, or junk bonds.

Diversification does not assure or guarantee better performance and cannot eliminate the risk of investment losses.

Income earned from municipal bonds is exempt from regular federal and in some cases, state and local income tax. Income may be subject to the alternative minimum tax (AMT).

Dividends are not guaranteed.

The laddering strategy does not assure or guarantee better performance than a non-laddered portfolio and cannot eliminate the risk of investment losses.

Class I shares may not be available to all investors. Minimum investments for the I share class may be higher than those for other classes.

There is no guarantee that the Fund will meet its investment objectives.

Please see our glossary for a definition of terms.

Thornburg mutual funds are distributed by Thornburg Securities Corporation.

Thornburg Investment Management, Inc. mutual funds are sold through investment professionals including investment advisors, brokerage firms, bank trust departments, trust companies and certain other financial intermediaries. Thornburg Securities Corporation (TSC) does not act as broker of record for investors.