The 174A catch-up looks like one multiplication — a balance times a tax rate. The problem is that both the "cap it at taxable income" rule and the time-value difference between 2025 and 2026 are easy to skip when you are doing the arithmetic once, in a spreadsheet cell, rather than running both election paths side by side.
| Step | Common mistake by hand | What this calculator does |
|---|---|---|
| Capping the deduction | Multiplies the full deduction by the tax rate, even when the deduction is bigger than that year's taxable income. | Caps the usable deduction at that year's taxable income before the deduction, and flags the excess as an NOL risk rather than counting it as cash saved. |
| Comparing the two paths | Compares nominal dollars only, missing that a 2025 dollar is worth more than a 2026 dollar. | Computes the present value of each path's combined savings at an adjustable discount rate, and states the dollar and percentage difference. |
| Which election this even is | Confuses the 2025-return 1-year/2-year choice with the separate retroactive election to amend 2022-2024 returns, whose window closed July 6, 2026. | Only models the live 2025-return choice, and says so explicitly. |
| Rate assumptions | Assumes the same rate in both years, even when a bracket change is expected. | Takes separate 2025 and 2026 rates and income, and names when the two disagree enough to matter. |
| Is anything I enter uploaded anywhere? | N/A | No. The calculator runs entirely in your browser; nothing is sent to a server. |
Forgetting that a deduction can only produce an immediate cash tax saving up to that year's taxable income before the deduction. A hand estimate often multiplies the whole deduction by the tax rate and calls that the saving -- but if the deduction is bigger than the year's income, the excess does not vanish or convert to cash; it can create or increase a net operating loss instead, which is a different (and generally less valuable) outcome.
Comparing the two elections on nominal dollars alone. If your 2025 and 2026 rates and income are similar, the 1-year and 2-year paths can add up to about the same total tax saving on paper -- but a dollar saved in 2025 is worth more than a dollar saved in 2026, so a nominal-only comparison misses the time-value difference between the two paths.
Confusing the 1-year-vs-2-year choice on the 2025 return with the separate retroactive election to amend 2022-2024 returns directly. That retroactive path existed under the same Rev. Proc. 2025-28, but its election window closed July 6, 2026. The live choice today is only between taking the remaining balance entirely in 2025 or splitting it across 2025-2026.
Assuming the same marginal or effective rate applies in both years. A business anticipating a bracket change -- higher income, a change in entity structure, or a different mix of income -- can get a meaningfully different answer than one assuming a flat rate, and a hand estimate often skips modeling the two years separately.
No. Neither this calculator nor a by-hand worksheet built from this page knows your full return -- other deductions, credits, AMT, self-employment tax, or state conformity to Section 174A, which varies by state. Neither verifies your small-business eligibility (the $31 million average-gross-receipts test) or models net operating loss carryforward value. Both apply the same published Rev. Proc. 2025-28 election structures to the numbers you enter; verify against the IRS's own guidance or a qualified tax professional before relying on either.