Installment Sale Calculator: Year-by-Year After-Tax Breakdown

An installment sale under IRC § 453 spreads your capital gain across years as you receive payments — but the mechanics are more nuanced than they appear. Depreciation recapture is always recognized in the year of sale regardless of payment schedule. If your seller note exceeds $5 million outstanding, § 453A imposes an annual interest charge on your deferred tax. Enter your deal numbers to see exactly what you keep, year by year, and how that compares to taking a lump sum.

How the gross profit ratio works

The IRS doesn't let you recognize gain evenly over time — it uses a gross profit ratio (GPR), sometimes called the gross profit percentage. Your GPR equals your total installment-eligible gain divided by the total contract price (typically the sale price). Every principal payment you receive is multiplied by the GPR to determine how much gain you recognize that year.

If your GPR is 93%, then for every dollar of principal you receive, $0.93 is taxable capital gain and $0.07 is tax-free return of basis. On a $1.4M annual principal payment, you recognize $1.302M as capital gain — not $1.4M. The interest you earn is always ordinary income, regardless of the GPR.³

Key point: depreciation recapture is excluded from the installment gain for GPR purposes — it is pulled forward to year one under § 453(i). The GPR applies only to the portion of gain above the recapture amount.

The § 453(i) recapture trap — year one, always

This is the most important rule to understand before you negotiate deal structure. All § 1245 and § 1250 depreciation recapture is recognized as ordinary income in the year of sale — even if you haven't received the cash yet.⁴

Practical example: you carry a 5-year note with 20% down on a $10M deal. Your business had $2M of accumulated depreciation on equipment. You receive $2M at close. Your federal tax on that recapture alone: $2M × 37% = $740,000 — due April 15, funded entirely from that down payment. The remaining installment gain gets deferred normally.

For asset-heavy businesses (manufacturing, construction, medical practices with expensive equipment), § 1245 recapture can represent the majority of total gain — sharply limiting what the installment method can defer. Run the numbers before you structure the deal.

§ 453A: the interest charge on large seller notes

Section 453A creates an annual interest charge when your outstanding installment obligations exceed $5 million at the close of any tax year.⁵ The mechanics:

• The charge applies only to the portion of outstanding obligations above $5 million
• Formula: applicable percentage × deferred federal tax liability × § 6621 underpayment rate
• The IRS underpayment rate (§ 6621(a)(2)) for Q2 2026 is 6%⁶
• The charge is paid with your annual federal return — it is not deductible
• It accrues every year the note balance stays above $5M

On a $10M seller note with $6M of unrecognized gain taxed at 23.8%, year-one § 453A is approximately: ($10M − $5M) / $10M × ($6M × 23.8%) × 6% = 50% × $1.428M × 6% = $42,840. This is real money that erodes the deferral benefit, and it accrues annually until the balance drops below $5M. Increasing the down payment is the most direct way to reduce this charge.

When installment sale deferral makes sense

• Seller financing is required to close the deal. In the $2–15M market, buyers frequently need a seller note as part of the capital stack. If carrying paper is what closes the deal at your price, installment treatment is the natural result — you're not choosing it independently.
• Spreading gain reduces your tax bracket exposure. If recognizing all gain in one year pushes you into the 23.8% bracket but spreading it across years keeps some gain at 18.8% or 15%, you save real money. The benefit is 3.8 percentage points on the portion that stays below the NIIT threshold — roughly $38,000 per $1M shifted.
• Post-sale state relocation. If you plan to move from a high-tax state (CA, NY) to a no-tax state (FL, TX, NV) before future payment years, the installment method can capture the state rate savings on those later payments. Timing matters: you must establish domicile before the payment year, and CA actively challenges these transitions.
• You have offsetting items in future years. Capital loss carryforwards, large charitable deductions, or NOL carryforwards in future years can absorb installment gain more efficiently than recognizing everything at once.

When to consider electing out

You can opt out of installment treatment and recognize everything in the year of sale — elect out by the extended return due date.³ This makes sense when:

• You have large capital losses or loss carryforwards that offset the gain this year, making immediate recognition cheap
• You believe capital gains rates will rise — lock in current rates now
• The § 453A interest charge exceeds your deferral benefit (common with large notes and modest gain rates)
• California residency: CA does not conform to the federal installment method for California-source gain. CA residents may owe California tax in the year of sale regardless — partially defeating the deferral strategy