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What it calculates: Total itemized deductions, Should you itemize? (1 = yes, 0 = take standard), Extra tax saved vs standard, Deduction you would claim.
Updated 5 June 2026 · Transparent assumptions
The standard deduction was already giving you $16,100 for free
The itemised total comes to $19,000 against a standard deduction of $16,100. Itemising wins, but only by $2,900 — and at a 22% rate that extra deduction saves $638. The first $16,100 of itemised expenses achieved nothing, because that much was available without any of it.
This is the threshold effect that makes deduction planning counterintuitive. Deductible spending below the standard amount has no tax value whatsoever, and spending just above it has very little. The marginal tax benefit of a charitable gift is zero until your other deductions have already cleared the standard deduction.
Two years of giving in one year can clear a bar that neither year would
If your itemised deductions sit just below the standard deduction every year, you never benefit from any of them. Concentrating two years of discretionary deductible spending — charitable giving is the usual candidate — into a single year can push that year well above the threshold while the other year takes the standard deduction.
The same total spending, differently timed, produces a deduction where none existed. Donor-advised funds exist largely to make this practical: contribute and deduct in the bunching year, distribute to charities over the following years. Whether it is worth doing depends on how far below the threshold you normally sit.
Every line has its own rules, and most have limits
Mortgage interest is usually deductible only on debt up to a cap and only on a qualifying residence. State and local taxes are capped in the US at a fixed amount that applies regardless of filing status. Medical expenses are deductible only above a percentage-of-income floor, so the first several thousand typically counts for nothing.
Charitable deductions have their own ceilings as a share of income, with carryforward for the excess, and require substantiation above modest amounts. Entering gross figures for each category without applying these limits will overstate the itemised total, sometimes enough to reverse the decision this page computes.
Current-year rules, one marginal rate, and no state interaction
The standard deduction and every category limit change between years and between jurisdictions. The saving is also computed at a single marginal rate, which understates the benefit where the extra deduction crosses into a lower band.
A further complication is that some jurisdictions require you to itemise on the state return only if you itemised federally, or allow itemising on one and not the other. The optimal choice is occasionally to itemise federally at a small loss in order to itemise at state level at a larger gain — a calculation this page does not attempt.
Sources & References
Figures on this page are checked against primary, authoritative sources. Links open in a new tab.
Tax rules vary by country, state, tax year, filing status, income type, deductions, and exemptions. This calculator is educational and uses the values you enter. Always verify final tax treatment with official sources or a qualified tax professional.
Published the calculator with its formula, worked example, assumptions, limitations and a bespoke guide, and added an automated formula test suite covering it.
Tested that the larger of the two deductions is always the one used, and that the extra saving is measured against the standard deduction rather than from zero.
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