Original Issue Discount on Municipal Bonds

An original issue discount on a municipal bond occurs when a bond is issued below par (face value), and the discount accretes—builds up—over the bond’s life until maturity at par. Unlike taxable bonds, the accrued OID on a muni is not subject to federal tax, making munis especially attractive to high-bracket investors. However, buying a muni in the secondary market after issue complicates the picture: accrued versus original OID gets special treatment, and selling before maturity can trigger capital gains.

How OID Accretes at Issuance

A municipal bond issued with an original issue discount is sold by the issuer below par. If a 20-year muni with $1,000 par value is issued at $900, the $100 discount is the OID. This discount accretes—mathematically increases each year—until the bondholder receives the full $1,000 par value at maturity.

The accretion method depends on the bond’s structure. Most bonds use constant-yield (scientific) accretion, which accounts for the compounding of the discount over time. Some use ratable (straight-line) accretion. Under constant-yield, the accretion is smaller in early years and larger in later years, reflecting the yield earned on the growing bond value.

From a bondholder’s perspective, each year the accrued OID represents “income”—the increase in the bond’s value. Federal tax law treats original OID on municipal bonds as tax-exempt; the accrual is not subject to federal income tax, even though you don’t receive a check for it. This makes OID munis particularly valuable to high-bracket taxpayers who want tax-free accumulation.

Tax Treatment of Original OID

The key advantage: original OID accrual is exempt from federal taxation. This applies only to munis that were issued with a discount (original OID), not munis purchased at a discount in the secondary market.

If you buy an OID muni at original issue and hold it to maturity, you receive no interest payments during the life of the bond (if it’s a zero-coupon muni) or interest plus accretion. At maturity, the issuer pays you par, and you owe no federal tax on the discount accretion. Your tax gain—if any—comes only if you sold the bond before maturity for more than your purchase price.

This tax-free treatment is a major reason institutional and high-income investors favor OID munis. The accrual compounds tax-free, which is equivalent to earning a significantly higher after-tax yield on a taxable bond.

Secondary Market Purchase and Market Discount

Complications arise when you buy a muni in the secondary market after original issuance. Suppose an OID muni originally issued at $900 is now trading at $950 two years later. If you buy it at $950, you face a split:

• Original issue discount (issued at $900, par $1,000): the original $100 discount is partially accrued and partially remains; the remaining portion is original OID and accretes tax-free
• Market discount (your purchase at $950, par $1,000): the $50 difference between your purchase price and par is market discount, and its accrual is taxable

The IRS treats them differently. Original OID continues to accrete tax-free. Market discount accrues as ordinary income (not capital gains) as the bond approaches maturity, unless you make an election to accrue it annually.

Market Discount Election and Accrual

If you buy a muni at a market discount, you have two choices:

Without election (defer accrual). You pay no tax on the market discount until you sell the bond or it matures. If you sell for a gain, the gain is taxed as ordinary income, not as capital gain.

With market discount election. You elect to accrue the market discount annually over the bond’s remaining life. Each year, a portion of the market discount is included in gross income and taxed at ordinary tax rates. At maturity or sale, the remaining accrued amount adjusts your basis, potentially reducing or eliminating any gain.

The election is binding and applies to all future debt obligations you acquire with market discount. Most investors skip the election for munis (since interest is tax-free anyway) but make the election for taxable bonds (to convert ordinary-income accrual into capital-gain treatment at sale).

Accrual Rate and Remaining Life

The accrual of market discount is calculated based on the bond’s remaining time to maturity. If you buy a bond two years into a 20-year maturity, the market discount accrues over the remaining 18 years, not the full 20.

The accretion method is typically constant-yield, matching the bond’s yield-to-maturity at purchase. Under constant-yield, accrual is higher in later years. A bond bought at a steep market discount accrues more in year 18 than in year 1, reflecting the compounding effect of the underlying yield.

Example: Tracing Original OID Through Secondary Market

Assume a 10-year, zero-coupon muni:

• At issue: Par $1,000, issued at $500 (original OID = $500)
• Bond constant-yield accretes at 7.2% annually
• Year 2: Bond value approximately $575; you buy it at $575
  • Original OID remaining to accrete: approximately $425 (from $575 to $1,000)
  • This $425 is original OID and accretes tax-free
  • Your purchase price: $575
  • Market discount: $1,000 − $575 = $425
  • But the $425 is offset by the original OID, so there is no separate market discount
• Year 10: Bond reaches par $1,000; you receive it
  • You paid $575; you received $1,000; gain is $425
  • Because the gain came from original OID accrual (tax-free) + market discount (taxable if elected or deferred), your treatment depends on your election
  • Without election: the $425 is treated as ordinary income at maturity or sale
  • With election: the $425 is accrued annually as ordinary income

The exact treatment hinges on how much of the gain is original OID (tax-free) versus market discount (taxable).

Selling Before Maturity

If you sell a muni with OID before maturity, the accrued gain is split:

• Accrued original OID: tax-free
• Accrued market discount (if applicable): taxed as ordinary income
• Price appreciation or depreciation beyond accrual: taxed as capital gain or loss

If you bought at $575 and sold two years later at $650, your $75 gain would be allocated between accrued OID (tax-free), accrued market discount (ordinary income), and capital appreciation (capital gain), depending on the exact accrual schedules.

This is why many investors hold OID munis to maturity: the accrual is predictable, and the tax treatment at the coupon level is clear. Selling early requires careful tracking of accrual and requires distinguishing between income types.

Reporting and Record-Keeping

The bond issuer or your broker provides Form 1099-INT or a similar statement showing OID accrual for the year. For original OID purchased at issue, the accrual is clearly marked as municipal (tax-exempt). For secondary-market purchases, the statement should separate original OID from market discount.

Keep detailed records of your purchase price, date, and the OID accrual schedule. If you sell, you’ll need to calculate your basis (purchase price + any accrued OID you’ve already paid tax on, if applicable, minus any capital losses) to determine your gain or loss.

The IRS can impose penalties if OID is misreported, so maintaining accurate records is important if you’re a frequent trader or have a large muni position.

See also