How the §453 Installment Method Actually Calculates Gain --- A Worked Example

A step-by-step look at the gross profit ratio, year-by-year gain recognition, and where the deferral benefit really comes from

April 29, 2026

When a client tells me they are selling an investment property or a privately held business, the conversation usually turns within a few minutes to taxes. Most people have heard that an "installment sale" can spread the tax bill out over several years. Far fewer have actually seen the arithmetic. The calculation isn't complicated, but it has a few moving parts that catch sellers off guard --- and the easiest way to understand them is to walk through a real worked example, beginning to end.

This piece does exactly that. We'll build a §453 installment sale from the sale price up, compute the gross profit ratio, walk through five years of payments, separate the interest from the principal, and compare the result to a lump-sum sale. The example is small on purpose --- $4 million rather than $25 million --- so that every number can be checked on a calculator and the mechanics stay visible without §453A or other large-deal complexities crowding the picture.

The whole installment method rests on one number: the gross profit ratio (often called the "gross profit percentage"). The IRS defines it the same way every time. You take the gross profit on the sale --- the contract price minus the seller's adjusted basis, including any selling expenses --- and you divide it by the contract price [1]. That ratio tells you what fraction of every principal dollar the seller receives is taxable gain. The rest of the dollar is a tax-free recovery of basis.

The reasoning is pure proration. The seller's basis is treated as already paid for: the law lets the seller pull that basis back out of each payment first, in proportion. If a seller's gross profit ratio is 80 percent, then 80 cents of every principal dollar received is taxable gain, and 20 cents is a return of cost.

Two things that often surprise people. First, the gross profit ratio is fixed at the moment of sale and does not change as payments come in. If the buyer pays early, more gain hits sooner; if the buyer pays late, more gain hits later. The ratio itself is constant. Second, the interest the buyer pays on the deferred portion is taxed completely separately --- as ordinary interest income, the same as a corporate-bond coupon would be taxed. It is not part of the gain calculation at all [1].

Picture a client who sells a long-held investment property for $4,000,000. After all the depreciation and improvements have been accounted for, her cost basis is $800,000. (Assume for the moment there is no depreciation recapture --- we'll come back to that.) The gross profit on the sale is therefore $3,200,000. The contract price is $4,000,000.

The gross profit ratio is $3,200,000 divided by $4,000,000, or 80 percent.

The buyer puts $800,000 in cash on the table at closing and gives the seller a promissory note for the remaining $3,200,000, payable in four equal annual principal installments of $800,000 each. The note bears interest at 5 percent on the outstanding balance, paid annually with each principal payment. (Five percent is illustrative; in any real deal, the parties have to use at least the applicable federal rate to avoid imputed interest under §1274 [2].)

So the seller will receive five total cash payments: $800,000 at closing in year zero, then $800,000 of principal plus accrued interest at the end of each of years one through four.

Year zero is closing. The seller receives $800,000 of cash. Because the gross profit ratio is 80 percent, $640,000 of that payment is long-term capital gain and the remaining $160,000 is a tax-free recovery of basis. There is no interest in year zero because no time has elapsed.

Year one: the seller receives $800,000 of principal, plus interest of $160,000 (5 percent of the $3,200,000 outstanding note). The principal payment splits exactly the same way as the closing payment: $640,000 of long-term capital gain and $160,000 of basis recovery. The $160,000 of interest is taxed separately as ordinary interest income.

Year two: another $800,000 of principal, plus interest of $120,000 (5 percent of the now-$2,400,000 outstanding balance). Again $640,000 of gain, $160,000 of basis, $120,000 of ordinary interest.

Year three and year four are mechanically identical: $800,000 of principal split 80/20 into $640,000 of gain and $160,000 of basis recovery, plus a shrinking interest payment ($80,000 in year three on $1,600,000 outstanding, then $40,000 in year four on the final $800,000). At the end of year four, the note is retired.

Add up the gain recognized: five payments of $640,000 each equals $3,200,000 --- exactly the original gross profit. Add up the basis recovered: five payments of $160,000 each equals $800,000 --- exactly the original basis. The math closes to the penny. Figure 1 shows the breakdown of each year's $800,000 principal payment between gain and basis recovery.

Figure 1: Each $800,000 principal payment splits 80/20 --- $640,000 of long-term capital gain and $160,000 of tax-free recovery of basis. The gross profit ratio is fixed at the moment of sale and applies the same way to every payment.

For a high-income seller, the all-in federal rate on long-term capital gain is 23.8 percent --- 20 percent at the top capital-gains bracket plus 3.8 percent for the Net Investment Income Tax [3][4]. Applied to $640,000 of gain per year, the federal capital-gains tax is roughly $152,320 each year, for five years.

Compare that to a lump-sum sale. If the same seller had taken the full $4,000,000 in cash at closing, the entire $3,200,000 of gain would be reported in year zero. At 23.8 percent, the federal tax bill is roughly $761,600 --- all due in the year of sale.

Notice the totals. Five years of $152,320 also adds up to $761,600. The installment method does not reduce the total federal capital-gains tax. It only spreads it out. Figure 2 shows the cumulative federal tax paid under each path. Both lines end at the same place; the installment line just gets there more slowly.

So where does the benefit actually come from? Three places, in roughly the order I see them matter. First, time value of money --- a dollar of tax paid in year four is meaningfully cheaper in present-value terms than a dollar paid today. Second, bracket and NIIT control: if the seller's other income drops in the years after the sale, some of the gain may now sit beneath the NIIT threshold or in a lower capital-gains bracket. Third, coordination with other planning. If the seller has charitable deductions lined up over the next several years, or planned Roth conversions, spreading the gain creates room to absorb each year's piece against those offsets.

Figure 2: Cumulative federal capital-gains tax under each path. The lump-sum sale recognizes the full $3.2M gain in year zero. The installment method spreads the tax across five payments. Both totals reach $761,600 --- only the timing differs.

The mechanics above are the whole installment-method gain calculation. They are clean and well-defined. But three real-world wrinkles can pull money out of the deferral that the gross profit ratio doesn't capture.

Depreciation recapture comes first. To the extent the gain on a sale represents prior depreciation deductions on §1245 property (most equipment) or §1250 property (most real-estate improvements), the recapture portion has to be reported in the year of sale, not deferred [1]. A seller can defer the appreciation; not the recapture.

Section 453A is the second. Once the face amount of the deferred installment obligations a non-dealer holds at the end of the year of sale exceeds $5 million, the IRS imposes an annual interest charge --- floating with the §6621 underpayment rate --- on the portion of the deferred tax attributable to the obligations above that threshold [5][6]. Our $4 million example sits cleanly below the threshold; a $25 million example does not.

The pledge rule is the third. If the seller pledges the installment note as collateral for a loan, the proceeds of the pledge are generally treated as a payment on the note --- accelerating gain recognition without an actual sale of the note [1]. Promoters of "monetized installment sale" structures occasionally try to engineer around this rule, with results the IRS and Tax Court have not been kind to.

The §453 installment method is one of the most-used and least-understood provisions in the tax code. The arithmetic itself is a single ratio applied across every payment --- in our example, 80 cents of gain and 20 cents of basis, year after year, until the note pays off. The interest is separate. The total tax doesn't change; only the timing does. And once a deal is large enough to trip §453A, or contains depreciation recapture, the deferral benefit is partly priced back to the seller before the first payment arrives.

The reason to walk through the math in a worked example is so the seller can see what is and isn't being deferred before the term sheet is signed. We model the actual cash-tax curve rather than the brochure version and coordinate it with the seller's other planning levers. If you are thinking about a sale, the time to run these numbers is well before the closing date, while the structure is still negotiable.

This piece is educational. The specifics of any sale require a conversation with your attorney, your CPA, and Perissos.

All my best,

Brandon VanLandingham, CFA, CMT, CFP

[1] IRS Publication 537 (2025), Installment Sales, https://www.irs.gov/publications/p537.

[2] IRC §1274; IRS, Applicable Federal Rates, https://www.irs.gov/applicable-federal-rates.

[3] Rev. Proc. 2024-40, 2025 inflation adjustments (long-term capital gains rate breakpoints), via Tax Foundation summary, https://taxfoundation.org/data/all/federal/2025-tax-brackets/.

[4] IRS Topic No. 559, Net Investment Income Tax, https://www.irs.gov/taxtopics/tc559.

[5] IRC §453A; IRS LB&I Process Unit, Interest on Deferred Tax Liability, https://www.irs.gov/pub/fatca/int_practice_units/interest-on-deferred-tax-liability.pdf.

[6] Rev. Rul. 2025-22, Section 6621 Determination of Rate of Interest (first quarter 2026 underpayment rate of 7 percent), https://www.irs.gov/pub/irs-drop/rr-25-22.pdf.

This piece is educational. It is not legal, tax, or accounting advice and is not a recommendation to take or refrain from any specific action. Tax law is fact-specific and changes regularly. Please coordinate any decisions discussed here with your attorney, your CPA, and Perissos before acting.

Perissos Private Wealth Management is a Registered Investment Adviser ("RIA"). Registration as an investment adviser does not imply a certain level of skill or training, and the content of this communication has not been approved or verified by the United States Securities and Exchange Commission or by any state securities authority. Perissos Private Wealth Management renders individualized investment advice to persons in a particular state only after complying with the state's regulatory requirements, or pursuant to an applicable state exemption or exclusion. All investments carry risk, and no investment strategy can guarantee a profit or protect from loss of capital. Past performance is not indicative of future results.

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