Section 453A Interest Charge: Calculator and Plain-English Guide

How the interest charge works, in plain English

An installment sale lets you pay tax as the buyer pays you. On very large notes, Congress decided that deferral should not be interest-free. Section 453A charges interest on the tax you have not yet paid, but only on the share of your notes above $5 million.

The test has three parts (453A(b)):

1. $150,000 floor. The note must come from a disposition with a sales price over $150,000. Sales that are part of the same transaction or a series of related transactions count as one sale.
2. $5 million year-end test. The face amount of all such notes that arose during the tax year and are still outstanding at the close of that year must exceed $5,000,000. Exactly $5,000,000 does not trigger it.
3. Not exempt. Farm property, personal-use property sold by an individual, and qualifying timeshares and residential lots are excluded.

If a note is caught in its first year, it stays caught. The charge is figured again at the end of every year the note is outstanding (453A(c)(1)).

The formula, step by step

Interest = deferred tax liability × applicable percentage × underpayment rate (453A(c)(2)).

• Deferred tax liability (453A(c)(3)): the gain not yet recognized at year end, times the maximum tax rate under Section 1 (or Section 11 for corporations). For an individual that is 20% on long-term capital gain. IRS Publication 537 tells you to use the maximum rate as appropriate to the type of gain; the engine on this page uses 25% for any unrecaptured Section 1250 gain still in the note. The 3.8% net investment income tax is not part of the formula.
• Applicable percentage (453A(c)(4)): face amount of the year's notes outstanding at year end above $5,000,000, divided by that total face amount. A $10,000,000 note gives 50%. A $6,000,000 note gives 16.7%. Per Publication 537, this percentage is computed in the year of sale and used for all later years, even as the balance falls.
• Underpayment rate: the Section 6621(a)(2) rate for the month in which your tax year ends. For a calendar-year individual, that is the December rate. The IRS kept it at 7% for the quarter beginning October 1, 2026. It resets quarterly, so later years may differ.

The unrecognized gain each year is simply the remaining principal times the gross profit percentage from Form 6252, line 19.

Who it hits, and who it does not

• Hit: individuals and entities carrying more than $5 million of new notes at year end from sales of commercial real estate, rental portfolios, operating businesses or investment land.
• Not hit: farm property. Property used or produced in the trade or business of farming (as defined in Section 2032A(e)(4) and (5)) is excluded by 453A(b)(3)(B). A seller-financed farm or ranch can carry a large note with no 453A interest.
• Not hit: personal-use property sold by an individual (453A(b)(3)(A), using the Section 1275(b)(3) definition).
• Not hit: timeshares and residential lots under 453(l)(2)(B). Those follow their own interest rule in 453(l)(3).
• Not hit: notes under the threshold. A seller whose year-end face amount is $5,000,000 or less owes nothing under 453A(a)(1), though the Section 453A pledge rule still applies to any note from a sale over $150,000.

Related businesses are combined: persons treated as a single employer under Section 52(a) or (b) are treated as one person for the $5 million test. Spouses are a different question, covered below.

Worked example (engine-computed)

Assumptions (illustrative): individual seller, calendar year 2026, nonfarm commercial building sold for $12,000,000. Adjusted basis $4,000,000 after $2,000,000 of straight-line depreciation. No selling costs shown. $2,000,000 down, $10,000,000 note paid $1,000,000 of principal a year for 10 years. Underpayment rate held at 7% every year (it will move).

• Gross profit $8,000,000; gross profit percentage 66.67%.
• Year 1 gain recognized: $1,333,333, all unrecaptured Section 1250 gain because that layer is reported first.
• Unrecognized gain at year end: $6,666,667 ($666,667 unrecaptured Section 1250 plus $6,000,000 other long-term gain).
• Deferred tax liability: $666,667 × 25% + $6,000,000 × 20% = $1,366,667.
• Applicable percentage: ($10,000,000 minus $5,000,000) / $10,000,000 = 50%, locked for the life of the note.
• Year 1 interest charge: $1,366,667 × 50% × 7% = $47,833.

Total over the note: $257,833 of nondeductible interest at a steady 7%. Note that the charge continues even after the balance drops below $5 million (years 6 to 10), because the 50% applicable percentage was fixed in year one.

Same sale, two other facts:

• Farm property: $0 interest charge (453A(b)(3)(B)).
• Spouses each own half: each spouse holds a $5,000,000 note. Neither exceeds $5,000,000, so the engine shows a 0% applicable percentage and $0 charge for each, if spouses are tested separately (see IRS stance below).

Engine: a453aPercentage and a453aCharge. Use the calculator on this page to run your own numbers.

Planning moves that change the charge

• Ownership between spouses. Each taxpayer has a separate $5 million threshold, and the IRS concluded in Technical Advice Memorandum 9853002 that married individuals are not treated as one person for this test. Property already owned jointly or as community property may give two thresholds. A transfer between spouses made shortly before a sale should be reviewed by your CPA and attorney for real ownership and timing.
• Down payment and note size. Every dollar of face above $5 million raises the applicable percentage. In the example, $7,000,000 down would bring the note to $5,000,000 and remove the charge, at the cost of more tax in year one.
• Tax-year timing. The test counts notes that arose in the same tax year. Unrelated sales that close in different tax years are tested separately. Splitting one deal artificially invites a step-transaction challenge.
• Farm property. Confirm the property meets the Section 2032A(e)(4) or (5) farming definition; if it does, the charge does not apply.
• Prepayment. Paying the note down faster shrinks the deferred tax each year, which shrinks the charge. The percentage stays fixed.
• Compare with electing out. Electing out of the installment method pays all the tax now and ends the charge. Usually deferral still wins, because only the share above $5 million carries interest, but it is worth the math.

IRS stance and audit risk

Section 453A is settled law and has been in the Code since 1987. The audit risk is in compliance, not in the concept:

• Omitting the charge. It is easy to miss in years two and later, because it keeps applying after the sale year. The IRS walks through a multi-year computation in Publication 537.
• Wrong percentage. Recomputing the applicable percentage each year on the lower balance understates it; Publication 537 fixes it in the year of sale.
• Deducting it. Publication 537 says individuals cannot deduct this interest. Corporations can deduct it in the year paid or accrued.
• Spousal threshold. TAM 9853002 is not precedent for other taxpayers, and an examiner in that case argued the opposite. Document ownership carefully.
• Pledging the note. Borrowing against it can trigger tax under 453A(d); see the pledge rule analysis.

Costs and fees

The charge itself is the cost: in the example about $47,833 in year one and $257,833 over ten years at 7%, paid with your return and not deductible for an individual. Compare it with the value of deferring $1,366,667 of tax in year one: half of that deferral carries interest at 7%, and half carries none. The note's own interest from the buyer, often at or above the applicable federal rate, is earned on the full principal. Other costs are your CPA's annual computation and any legal work on ownership or note terms.

How it compares with a Section 453 installment sale

Section 453A is not an alternative to a Section 453 installment sale; it is a toll on the largest ones. Under $5 million of year-end face per taxpayer, an installment sale defers tax with no interest charge. Above it, deferral still works, but part of it is charged at the IRS underpayment rate. Notes on farm property avoid the toll entirely. A 1031 exchange has no 453A charge but requires reinvesting in like-kind real property. A deferred sales trust is itself an installment sale to a trust, so 453A can apply to it as well. Good seller financing terms (down payment, first-position deed of trust or UCC lien, personal guarantee from the buyer's owners) matter more on a note this size. Related reading: depreciation recapture on an installment sale.

Frequently asked questions