Every April, millions of US households face the same fork in the road on Form 1040: do you claim the standard deduction, a flat number the IRS hands you by filing status, or do you itemize on Schedule A, adding up mortgage interest, state and local taxes, charitable gifts, and medical bills? This tax deduction calculator makes the choice in one screen. Enter your actual Schedule A line items, slide in your marginal tax rate, and the tool tells you whether itemizing saves you money — and exactly how many dollars.
How to Use
- Enter the Mortgage Interest Paid from your Form 1098. This is the interest line on your home loan, not the principal.
- Type your State & Local Taxes (SALT) — state and local income tax (or sales tax, whichever is larger) plus property tax. The calculator automatically applies the federal $10,000 SALT cap, so enter your real number even if it is higher.
- Add Charitable Gifts — cash donations and the fair-market value of non-cash gifts to qualified 501(c)(3) charities.
- Fill in Qualified Medical Expenses if you have large out-of-pocket bills; only the portion above 7.5% of your AGI is actually deductible, but enter the full amount for a quick estimate.
- Enter any Other Itemized Deductions — casualty losses in a federally declared disaster area and similar Schedule A lines.
- Set Your Standard Deduction to the 2024 amount matching your filing status: Single $14,600, Married Filing Jointly $29,200, Head of Household $21,900.
- Set your Marginal Tax Rate — the federal bracket your top dollar of income falls into (10, 12, 22, 24, 32, 35, or 37%).
The result card shows your total itemized deduction, the SALT line after the $10k cap, the recommended deduction, the gap between itemized and standard, and the actual federal tax saved by choosing one path over the other.
The Math Behind the Decision
The IRS lets you deduct whichever number is larger:
Itemized total = mortgage interest + min(SALT, $10,000) + charitable gifts + medical + other
If that total beats your standard deduction, itemize. The extra deduction — the gap between your itemized total and the standard deduction — is multiplied by your marginal tax rate to get the actual tax savings.
For example, a filer with $12,000 mortgage interest, $10,000 SALT, and $3,000 charitable gifts totals $25,000 of itemized deductions. The 2024 single standard deduction is $14,600, so itemizing is ahead by $10,400. At a 22% marginal rate, that is $2,288 of federal tax saved — real money. If the same filer had only $6,000 of total itemized deductions, the calculator would recommend the standard deduction and show $0 of savings from itemizing.
What Counts on Schedule A
- Mortgage interest — interest on a home acquisition loan up to $750,000 of principal for loans taken out after December 15, 2017 (the limit was $1 million for older loans).
- SALT — state and local income (or general sales) tax plus real-estate and personal-property tax, combined and capped at $10,000 per return ($5,000 if married filing separately).
- Charitable gifts — cash up to 60% of AGI, and most non-cash property up to 30% of AGI, to qualified organizations only.
- Medical expenses — only the amount above 7.5% of your adjusted gross income.
- Casualty and theft losses — only in federally declared disaster areas since 2018.
Unreimbursed employee expenses, tax-prep fees, and investment advisory costs used to be deductible, but the TCJA suspended those miscellaneous itemized deductions through 2025.
Examples
Example 1 — A homeowner who should itemize. A married couple filing jointly pays $12,000 in mortgage interest, has $14,000 of state income and property tax (capped at $10,000), and gives $3,000 to church and charity. Total itemized = $25,000. Their 2024 standard deduction is $29,200, so itemizing loses by $4,200 — the calculator recommends the standard deduction and shows $0 of itemizing savings. They should not bother collecting Schedule A receipts.
Example 2 — The same couple, one year later. After a raise and a refinance, their mortgage interest is $18,000, SALT stays capped at $10,000, and charitable gifts rise to $5,000. Total itemized = $33,000, beating the $29,200 standard by $3,800. At a 24% marginal rate, itemizing saves $912. Now Schedule A is worth filing.
Example 3 — A high-earner in a high-tax state. A single software engineer in California pays $60,000 in mortgage interest, $22,000 in state income and property tax (capped at $10,000), and donates $50,000 to a donor-advised fund. Itemized total = $120,000 against a $14,600 standard. The gap is $105,400; at a 32% marginal rate, itemizing saves roughly $33,728. The SALT cap alone costs them $12,000 of otherwise-deductible tax.
FAQ
Should I itemize or take the standard deduction?
Itemize only if your total Schedule A deductions exceed your standard deduction ($14,600 single, $29,200 married filing jointly, $21,900 head of household in 2024). This calculator compares the two automatically: if your itemized total is larger, itemize; otherwise the standard deduction is the better deal.
What is the SALT cap and how does it work?
The State and Local Tax deduction (SALT) lets you deduct state and local income (or sales) tax plus property tax, but only up to $10,000 per year ($5,000 if married filing separately). The cap applies automatically in this calculator — enter your real SALT number and it will be capped at $10,000 for you.
How much mortgage interest can I deduct?
You can deduct mortgage interest on a main or second home, but the loan principal is capped at $750,000 for loans originated after December 15, 2017. Older loans (through December 14, 2017) keep the higher $1 million cap. Home-equity loan interest is deductible only if the proceeds are used to buy, build, or substantially improve the home.
What is my marginal tax rate?
Your marginal rate is the bracket your last dollar of taxable income falls into. For 2024 single filers: 10% up to $11,600, 12% to $47,150, 22% to $100,525, 24% to $191,950, 32% to $243,725, 35% to $609,350, and 37% above that. Use the bracket of your top dollar, not your effective (average) rate.
Are charitable donations always deductible?
They are deductible only if you itemize and only to qualified 501(c)(3) organizations. You need a bank record or written receipt for any gift, and an acknowledgment letter for any single gift over $250. Cash gifts are limited to 60% of AGI; most non-cash gifts to 30% of AGI.
Do medical expenses count toward itemizing?
Only the portion above 7.5% of your AGI. If your AGI is $100,000 and you spent $12,000 on qualified medical bills, only $4,500 ($12,000 − $7,500) is deductible. Enter the full amount in this calculator for a quick estimate; your tax preparer will apply the AGI floor on Schedule A.
Disclaimer
This tax deduction calculator is provided for informational purposes only and does not constitute tax, legal, or financial advice. It estimates the Schedule A vs standard-deduction decision based on the inputs you enter and does not account for AGI limits, phase-outs, state-tax treatment, AMT, or special rules for high earners. The SALT cap ($10,000) and 2024 standard deduction amounts may change with new legislation. Always confirm your final deduction and file with a licensed tax professional or IRS-approved software before submitting Form 1040.