A Flexible Spending Account (FSA) is one of the most reliable tax breaks at work: you set aside pre-tax dollars before payroll taxes are applied, then spend them on qualified medical costs. The tradeoff is the famous "use it or lose it" rule. This FSA calculator shows exactly how much you would contribute, how much smaller each paycheck becomes, and how much federal and FICA tax you avoid — so you can fund the account generously without risking forfeiture.
Adjust the sliders and the result card updates instantly. Enter your expected annual medical spend and compare it against what you elect, so you never leave money on the table — or leave money on the shelf.
How to Use
- Enter your Annual FSA Contribution — the total salary reduction you elect for the plan year. The 2025 IRS limit is $3,300 per employee; going over it triggers a taxable excess contribution.
- Set your Marginal Tax Rate to your top federal bracket (12%, 22%, 24%, 32%, etc.). If your state taxes income, add your state marginal rate to be more precise.
- Choose your Pay Periods per Year — 12 for monthly paychecks, 24 for semimonthly, 26 for biweekly (the most common in the US), and 52 for weekly.
- Optionally enter Expected Medical Spend — recurring copays, prescriptions, dental, vision, and supplies. This is the budget you should not exceed.
The result card breaks the contribution into your per-paycheck reduction, the federal income tax you save, the FICA (Social Security and Medicare) tax you save, and the net cost after all savings. The single highlighted number to watch is Total Annual Tax Savings — that is your pure return on using the FSA.
How the FSA Math Works
FSA money leaves your paycheck before income and payroll taxes are calculated. That single fact drives every number on this page:
- Federal tax savings = annual contribution × your marginal tax rate.
- FICA savings = annual contribution × 7.65% (6.2% Social Security on wages up to the annual limit, plus 1.45% Medicare).
- Total tax savings = federal savings + FICA savings.
- Net cost = what you put in − what you saved in taxes.
Worked example on the maximum 2025 contribution of $3,300 at a 22% marginal bracket: federal tax savings are $3,300 × 0.22 = $726.00, FICA savings are $3,300 × 0.0765 = $252.45, for a total of $978.45 in annual tax savings. The net cost of funding the full account is $3,300 − $978.45 = $2,321.55. In other words, you spend $2,321.55 of real money to cover $3,300 of medical bills you would have paid anyway — a ~29.65% discount off your eligible expenses.
Because contributions are taken evenly across the year, a $3,300 annual election on 26 biweekly paychecks costs about $126.92 per paycheck, while on 12 monthly paychecks it costs $275.00 per month.
FSA vs HSA: Do Not Confuse Them
People mix these up constantly, but they behave very differently:
- FSA (this calculator) is an employer-sponsored plan tied to your benefits enrollment. It has a use-it-or-lose-it rule: any unspent balance at plan year end is forfeited (up to $660 may carry over under IRS 2025 rules, depending on your employer's plan). You do not own the account, it does not earn interest, and you cannot invest it.
- HSA pairs with a high-deductible health plan. Money is yours, rolls over forever, grows tax-free, and can be invested like a retirement account. There is no "use it or lose it."
If you have an HSA-eligible plan, an HSA is almost always the stronger long-term vehicle. An FSA shines when you have predictable near-term expenses — braces, glasses, copays, a planned surgery — and you want the instant 20–30% discount on those bills.
Examples
Example 1 — Funding the full $3,300 at 22%. A teacher earning in the 22% bracket elects the maximum 2025 FSA on biweekly pay. Each paycheck drops by $126.92, she saves $726.00 in federal tax and $252.45 in FICA, for a total tax savings of $978.45. Her expected spend is $2,800, so she keeps a small cushion under the $660 carryover limit.
Example 2 — A lower earner at 12%. A part-time worker elects $1,000 to cover glasses and contact lenses. At a 12% marginal rate, federal savings are $120, FICA savings are $76.50, for $196.50 in savings. Even at a low bracket, the FICA exclusion alone makes contributing worthwhile if the money will be spent on eligible items.
Example 3 — A high earner at 32%. A software engineer in the 32% bracket elects the full $3,300. Federal savings jump to $1,056, FICA to $252.45, for $1,308.45 in total savings — a ~39.65% effective discount. Higher tax brackets make FSA math dramatically more rewarding.
FAQ
How much can I put in an FSA in 2025?
The IRS 2025 employee contribution limit is $3,300. Employers may also allow a carryover of up to $660 of unused funds into the next plan year, or a 2.5-month grace period, depending on the plan documents. Contributions above the limit are treated as taxable income.
How much does an FSA reduce my take-home pay?
Divide your annual election by your number of pay periods. A $3,300 election costs about $275.00 per month (12 periods), $126.92 per biweekly paycheck (26 periods), or $63.46 per weekly paycheck (52 periods). Enter your own figures in the calculator above.
Is FSA money really tax-free?
Yes — contributions avoid federal income tax and FICA payroll tax (7.65%). Some states also exclude FSA contributions from state income tax, while others (such as California) do not. If your state taxes the contribution, add your state marginal rate to the tax-rate field for a more accurate savings estimate.
What happens if I don't spend all my FSA money?
Under the use-it-or-lose-it rule, unspent funds at the end of the plan year are generally forfeited. To soften this, the IRS lets plans either allow up to a $660 carryover or a 2.5-month grace period, but not both. Check your Summary Plan Description. This is why entering your expected medical spend matters: elect only what you are confident you will use.
What can I pay for with an FSA?
Qualified expenses include copays, deductibles, prescription drugs, dental and orthodontia, vision exams, glasses and contact lenses, crutches, bandages, pregnancy tests, and many over-the-counter medicines and menstrual products (thanks to the CARES Act). Cosmetic procedures, gym memberships, and most health insurance premiums are not eligible.
Can I have both an FSA and an HSA?
Usually not. If you are enrolled in an HSA-qualified high-deductible plan, you cannot have a general-purpose FSA, though a limited-purpose FSA (covering only dental and vision) is allowed alongside an HSA. If you have a regular FSA through a non-HDHP plan, you cannot contribute to an HSA.
When should I not max out my FSA?
If your expected annual spend is low and your employer does not offer a carryover or grace period, electing the full $3,300 risks forfeiting unused money. A good rule of thumb is to contribute what you expect to spend, plus a small buffer — not the legal maximum.
Disclaimer
This FSA calculator is provided for informational purposes only and is not medical advice, tax advice, or financial advice. Estimates are based on the inputs you enter and assume a federal marginal bracket plus the standard 7.65% FICA rate; state tax treatment, employer plan rules, carryover allowances, and the IRS annual limits may differ and change. Qualified medical expenses and eligibility rules are set by the IRS and your employer's plan documents. Always confirm your election, plan rules, and tax situation with a benefits administrator or qualified tax professional before enrolling.