Most business owners assume that each year’s retirement plan contribution belongs to that year’s tax return. One plan year, one deduction, repeat.
But the tax code is more flexible than that — and for defined benefit and cash balance plan sponsors, that flexibility creates one of the more powerful timing plays available: deducting two plan years’ worth of contributions in a single tax year.
Done correctly, an S corporation can deduct its 2024 plan year contribution and its 2025 plan year contribution on the same 2025 tax return. Nothing exotic, nothing aggressive — just two well-established rules pointed in the same direction. Here’s how it works, when it makes sense, and where it can go wrong.
The two rules that make it possible
Rule one: contributions are deductible in the year actually paid. This is the default rule, and it surprises people. A pension contribution is generally deductible in the taxable year the money is deposited — regardless of which plan year it funds. The familiar practice of deducting a contribution for the prior year is actually the exception, not the rule.
Rule two: the grace period is optional. That exception — the grace period that lets a contribution made by the tax return deadline count for the prior year — only applies if the employer affirmatively ties the payment back. Under longstanding IRS guidance, that means either claiming the deduction on the prior year’s return or designating the payment in writing as being on account of the prior year. No designation, no deduction claimed? The contribution simply falls under the default rule and is deducted in the year paid.
Put these together and something interesting emerges. The plan year a contribution funds and the tax year it’s deducted are two independent questions. Your actuary certifies the contribution to the 2024 plan year for funding purposes. Your CPA deducts it in 2025 because that’s when it was paid. Both are correct at the same time.
The mechanics, step by step
For a calendar-year S corporation with a calendar-year plan:
- Make the 2024 plan year contribution after March 15, 2025 (the unextended return deadline) but no later than September 15, 2025. The March date matters because a contribution made after the return deadline can’t relate back to 2024 — it must be deducted in 2025. The September date matters because that’s the minimum funding deadline for the 2024 plan year, and it doesn’t move for anyone.
- File the 2024 return without the defined benefit deduction. The 2024 tax year simply has no DB contribution deducted on it.
- Make the 2025 plan year contribution by the 2025 return deadline — March 15, 2026, or September 15, 2026 if the return is extended — and claim it on the 2025 return under the normal grace period rule.
- Deduct both on the 2025 return. The 2024 plan year contribution is deducted because it was paid in 2025. The 2025 plan year contribution is deducted because it was paid within the grace period and tied back.
An example
Dr. Rivera owns her orthopedic practice, taxed as an S corporation, and sponsors a cash balance plan alongside her 401(k). Her required cash balance contribution for the 2024 plan year is $230,000, and the actuary projects roughly $250,000 for the 2025 plan year.
In late 2024, Dr. Rivera signs an agreement to sell her ownership interest in an ambulatory surgery center. The sale closes in June 2025 and will add about $900,000 of income to her 2025 return. Her 2024 income, by contrast, was a fairly ordinary year.
Under the standard approach, she’d deposit the $230,000 in early 2025 and deduct it on her 2024 return — sheltering ordinary-year income — then deduct the $250,000 in 2026 for the 2025 year. Fine, but it wastes the opportunity sitting in front of her.
Instead, she waits until April 2025 — after the March 15 return deadline has passed — and deposits the $230,000. Her actuary certifies it toward the 2024 plan year on the funding schedule, comfortably ahead of the September 15, 2025 funding deadline. Her CPA files the 2024 return with no cash balance deduction. Then in early 2026, she deposits the $250,000 for the 2025 plan year within the grace period.
Her 2025 return now carries a $480,000 cash balance deduction — landing squarely on top of the surgery center gain, in her highest-income year, at her highest marginal rate. The plan received exactly the same dollars on a compliant schedule. Only the tax geography changed.
When this strategy earns its keep
The double deduction is a bunching play. You’re not creating a deduction out of thin air — you’re moving one deduction forward a year, which means the prior year goes without. That trade is worth making when the two years are meaningfully different:
A spike year. Business sales, real estate gains, unusually strong profits, large bonuses. Stacking $400,000–$600,000 of deductions against income taxed at the top bracket, rather than splitting it across two ordinary years, can be worth tens of thousands of dollars in permanent rate savings.
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A weak prior year. If 2024 income was too low to make full use of the deduction anyway — a down year, large losses elsewhere, income already below the top brackets — shifting the deduction into 2025 costs little and may gain a lot.
Bracket and threshold management. For S corporation owners, the deduction flows through to the personal return, where it can interact with the qualified business income deduction phase-outs, the net investment income tax, and other cliffs. Sometimes the value isn’t the rate differential — it’s landing on the right side of a threshold.
If the two years look roughly the same, the strategy is mostly a wash, and the simpler default pattern is usually better.
Where it goes wrong
Missing the funding deadline. The single non-negotiable date in this entire strategy is September 15, 2025 — the minimum funding deadline for the 2024 plan year. Waiting past March 15 to shift the deduction is deliberate; waiting past September 15 is a funding deficiency with excise tax consequences. The window is real but it is a window.
Accidentally tying the contribution back. If the corporation extended its 2024 return, a deposit made before September 15, 2025 is still capable of relating back to 2024. Discipline matters: don’t deduct it on the 2024 return, and don’t sign anything designating it as on account of the 2024 tax year. The cleanest execution avoids the ambiguity entirely — no extension, deposit after March 15.
Blowing through the deduction ceiling. Two years of contributions must fit within a single year’s maximum deductible limit. For defined benefit and cash balance plans that ceiling is generous — it’s built on 150% of the plan’s funding target plus a cushion — so two years of required contributions almost always fit. But “almost always” is not “always,” particularly for well-funded plans or sponsors maximizing contributions in both years. Amounts over the limit are nondeductible and trigger an annual excise tax until absorbed. This is a five-minute confirmation for your actuary. Get it in writing.
Forgetting the combined-plan limit. Sponsors who also make employer contributions to a 401(k) or profit sharing plan above 6% of compensation face a combined deduction limit across both plans. Doubling the DB deduction in one year makes that math tighter. Keeping DC employer contributions at or under 6% of pay in the stacking year usually sidesteps the issue.
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Coordination failure. This strategy requires the CPA, the actuary, and the plan sponsor to all be telling the same story: the actuary allocating the contribution to one plan year, the CPA deducting it in a different tax year, and everyone doing it on purpose. Most of the horror stories here aren’t technical failures — they’re a CPA who reflexively deducted the spring contribution on the prior-year return because that’s what happens every year.
Bottom line
The plan year a contribution funds and the tax year it’s deducted don’t have to match. For a business owner staring down an unusually high-income year, deliberately breaking that match — skipping the deduction in an ordinary year to stack two years of contributions against the spike — is one of the cleanest large-dollar timing strategies in the qualified plan world. The rules supporting it are decades old and the IRS’s own guidance acknowledges the mechanics.
But it’s a strategy with three moving parts and two professionals who each only see half the picture. If you’re contemplating a big income event and you sponsor a defined benefit or cash balance plan — or you’re considering adopting one before the event lands — it’s worth a conversation that puts the actuary and the CPA in the same room before any money moves.
