Bond Premium Amortization: Election, Reporting, and Basis

Bond premium amortization is the process of spreading the extra amount you paid above a bond’s face value across the years you hold it, using the constant yield method. For taxable bonds, you elect to amortize and the yearly amount offsets your interest income. For tax-exempt municipal bonds, you don’t get a deduction, but you’re still required to reduce your basis each year by the same calculated amount. Either way, the goal is the same: by maturity, your basis equals par, so you don’t manufacture a phantom loss on money you spent to buy a higher coupon.

When You Have a Bond Premium

You have a premium whenever you pay more than face value. Say you pay $10,400 for a bond with a $10,000 par value. The bond’s coupon rate is above current market rates, so the higher cash flow is worth the extra $400. That $400 is the premium.

The tax code splits the treatment by whether the bond’s interest is taxable or tax-exempt. For taxable bonds like corporate debt, amortizing the premium is optional under IRC Section 171(c)(1), which applies “only if the taxpayer has so elected.” For tax-exempt municipal bonds, Section 171(a)(2) forbids any deduction for the premium, but amortization and basis reduction are still mandatory.¹

Electing to Amortize on Taxable Bonds

You make the Section 171 election by offsetting interest income with the bond premium on your timely filed return for the first year you want it to apply, and by attaching a statement identifying the election.² The election is easy to make and hard to walk back. Three features tend to surprise people:

It covers every taxable bond you hold in the election year and every taxable bond you buy afterward. You can’t pick which bonds it applies to.²
Revoking it requires IRS approval through Form 3115, because the IRS treats a revocation as a change in accounting method.³
You can’t apply the election retroactively. If you elect in a later year for a bond you already owned, prior-year amounts stay unamortized.²

If you hold bonds through a brokerage, check your 1099-INT before assuming you haven’t elected. Brokers often amortize premium automatically for covered securities and report the amount in Box 11 unless you’ve told them in writing to stop.⁴ If your broker has been doing it and you’ve been reporting the net figures, you’ve effectively made the election.

Skipping the election is a legitimate choice for a taxable bond. You’ll report the full coupon as interest income and can claim a capital loss when the bond matures at par. Whether that’s better than annual amortization depends on your bracket and how you use capital losses.

Why Tax-Exempt Bonds Are Different

For a muni bond, no deduction is allowed for the premium. The interest is already outside gross income, and the IRS won’t let you also deduct what you paid to acquire that exempt income.¹ But you still have to reduce your basis each year by the amount the deduction “would have been” if the bond were taxable, under Section 1016(a)(5).⁵

The reason is straightforward. If you pay $10,400 for a $10,000 muni and don’t reduce your basis, redemption at $10,000 produces a $400 capital loss on money that funded tax-free income. Mandatory basis reduction closes that gap. By maturity, your basis equals par, and there’s no artificial loss to claim.

How the Constant Yield Method Works

The constant yield method is required under Treasury Regulation 1.171-2. It calculates each period’s interest as the bond’s actual yield to maturity applied to your current adjusted basis, so the percentage return stays constant even as the dollars change.⁶

Start by finding the yield to maturity as of your purchase date. That’s the discount rate that makes the present value of all remaining payments equal what you paid. Your broker or a financial calculator can produce it. The yield stays constant across the bond’s life and needs at least two decimal places of precision.⁶

Each period, three steps:

Multiply your current adjusted basis by the yield to maturity for the period. That’s your economic interest, what the bond actually earned.
Look at the coupon payment. On a premium bond, the fixed coupon is always larger than the economic interest.
Subtract economic interest from the coupon. The difference is the amortized premium for that period. It reduces both your reportable interest and your basis.

Worked Example

You buy a $10,000 face value corporate bond for $10,400, a $400 premium. The coupon is 5% annually, paid semi-annually. Your yield to maturity is 3% annually, or 1.5% per semi-annual period.

First period: you receive a $250 coupon ($10,000 × 5% ÷ 2). Economic interest is $10,400 × 1.5% = $156.00. Amortized premium is $250 − $156.00 = $94.00. You report $156.00 as taxable interest, and your adjusted basis drops to $10,306.00.

Second period: economic interest is $10,306.00 × 1.5% = $154.59. Amortized premium is $250 − $154.59 = $95.41. Basis falls to $10,210.59. Each period the amortized portion grows a bit larger, because a shrinking basis produces less economic interest against the same coupon. The percentage return stays fixed at 1.5% per period.

Keep a complete amortization schedule showing every period’s calculation. You’ll need it for your return, for any sale before maturity, and if the IRS asks.

Reading Your 1099-INT and Reporting on Schedule B

For taxable covered securities, the broker’s treatment of premium shows up two ways. Some brokers put the full coupon in Box 1 and the amortized premium separately in Box 11. Others report a net figure in Box 1, already reduced, and leave Box 11 blank.⁴ Check which method your broker used before you touch Schedule B, or you’ll double-count. For tax-exempt covered securities, the equivalent amortized figure appears in Box 13, and it exists to help you track your basis reduction even though it produces no deduction.

When you do need to show the adjustment yourself on Schedule B, the IRS format is specific:⁷

On line 1, list all interest income including the full coupon from your premium bonds.
Below your last line 1 entry, write a subtotal of the interest listed.
Below the subtotal, enter “ABP Adjustment” and the total amortizable bond premium for the year.
On line 2, enter the subtotal minus the ABP Adjustment.

The net figure on line 2 is your taxable interest. The amortization offsets interest income directly here; it isn’t an itemized deduction, so the benefit reaches you whether or not you itemize.

What Happens to Your Basis When You Sell or Hold to Maturity

Every dollar of amortized premium comes off your basis, taxable or tax-exempt. Section 1016(a)(5) requires it for any bond where you’ve taken the amortization deduction, and separately for the “would-have-been” amount on tax-exempt bonds.⁵

Hold to maturity and the arithmetic settles cleanly. Your basis converges to par, you get par back, and there’s no gain or loss.

Sell before maturity and basis tracking is where mistakes cost money. Say you bought at $10,400 and have amortized $200 of premium. Your basis is $10,200. Sell at $10,300 and you have a $100 capital gain, even though you received less than you originally paid. Investors who fail to reduce basis end up understating their gain, and the IRS treats that as a compliance error.

On tax-exempt bonds, the stakes run higher because the reduction happens whether or not you tracked it. Claiming a capital loss at redemption on a premium muni is the kind of error examiners look for.

Callable Bonds

Callable bonds shorten the horizon over which you might amortize, because the issuer can redeem early. The regulations handle this through “deemed exercise” rules. For a taxable bond, the issuer is deemed to exercise a call in the manner that maximizes the holder’s yield. For a tax-exempt bond, the rule reverses: the issuer is deemed to exercise in the manner that minimizes the holder’s yield.⁸ Holder options like a put right are deemed exercised to maximize the holder’s yield.

Practically, for a callable muni purchased at a premium, you often end up amortizing to the earliest call date, which pulls the basis reduction forward. If a call is actually exercised on a date different from the one you’ve been amortizing toward, you’ll need to adjust.

Mistakes That Trigger IRS Problems

Three errors show up repeatedly.

Ignoring basis reduction on tax-exempt bonds. There’s no annual deduction to jog your memory, so it’s easy to skip. But the IRS expects the reduction, and claiming a capital loss at maturity on a premium muni is exactly the kind of thing that gets caught.

Putting the amortization on Schedule A. It belongs on Schedule B as an offset to interest, not as an itemized deduction. That placement matters: on Schedule B, the benefit reaches you regardless of whether you itemize.

Assuming the Section 171 election is bond-by-bond. It isn’t. Once you elect, every taxable bond you own now or later is covered, and revoking requires an accounting method change filed with the IRS.³ Investors who thought they were making a per-bond decision sometimes find they’ve bound themselves to amortize on a portfolio where they’d rather not.

1
Office of the Law Revision Counsel. 26 U.S. Code 171 – Amortizable Bond Premium
2
eCFR. 26 CFR 1.171-4 – Election to Amortize Bond Premium on Taxable Bonds
3
Internal Revenue Service. Publication 550 (2025), Investment Income and Expenses
4
Internal Revenue Service. Form 1099-INT (Rev. January 2024)
5
Office of the Law Revision Counsel. 26 USC 1016 – Adjustments to Basis
6
eCFR. 26 CFR 1.171-2 – Amortization of Bond Premium
7
Internal Revenue Service. Instructions for Schedule B (Form 1040)
8
eCFR. 26 CFR 1.171-3 – Special Rules for Certain Bonds