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HSA vs FSA Calculator

See how much more an HSA can save you compared to an FSA.

How it is calculated

The tool puts the same contribution into both accounts and charges the FSA for the share of it you expect to lose.

tax savings = contribution × tax rate ÷ 100
HSA cost = contribution − tax savings
forfeited = contribution × forfeit % ÷ 100
FSA cost = contribution − tax savings + forfeited
HSA advantage = FSA cost − HSA cost = forfeited

The contribution is in dollars and both percentages are entered as plain numbers (24 for 24%). The tax rate is your marginal rate, the rate on your last dollar of pay. Both accounts get the same up-front tax saving, so the whole advantage comes from the forfeited share: it always equals contribution × forfeit %, and it is zero if you expect to spend everything. The HSA is assumed to lose nothing. The tool does not check yearly contribution limits, whether you qualify for an HSA, any employer contribution, or investment growth inside an HSA.

Worked example

You plan to contribute $3,000, your marginal tax rate is 24% and you expect to leave 10% of the FSA unspent. Tax savings = 3,000 × 0.24 = $720.00. HSA effective cost = 3,000 − 720 = $2,280.00. Forfeited FSA money = 3,000 × 0.10 = $300. FSA effective cost = 2,280 + 300 = $2,580.00. The HSA advantage is 2,580 − 2,280 = $300.00, which is simply the forfeited amount. If you expected to use all of the FSA, the two would cost the same.

Try this example →

Common mistakes

  • Entering the average tax rate instead of the marginal rate. The saving comes from the bracket on your last dollars, so the average rate understates it.
  • Expecting the tax rate to change which account wins. It lowers both costs equally; only the forfeit percentage creates a difference.
  • Setting the forfeit percentage to 0 "to be safe" and then reading no advantage as proof the accounts are equal. The tool ignores HSA investment growth, portability and eligibility, which are real differences.
  • Entering a contribution above what is allowed for the year. The tool accepts any positive amount and does not check limits, so verify the allowed maximum separately.
  • Treating the HSA advantage as money received. It is the avoided loss on unspent funds, not a payment to you.

About this calculator

This calculator compares the effective net cost of putting money into a Health Savings Account (HSA) versus a Flexible Spending Account (FSA) for the same medical expenses. Both reduce your taxable income by the contribution amount, but they differ in what happens to unused funds: HSA balances roll over indefinitely and stay yours even if you change jobs, while most FSAs are subject to a use-it-or-lose-it rule (with only a small carryover or grace period allowed by the IRS), so unspent FSA money is typically forfeited.

US employees choosing between benefits during open enrollment use this comparison to see past the identical up-front tax savings and into the real difference: an HSA (only available with a qualifying High-Deductible Health Plan) has more long-term value if spending is unpredictable, since nothing is lost, while an FSA can still make sense for known, predictable annual expenses like orthodontia or a stable prescription. Benefits advisors and HR teams reference this same forfeiture-risk logic when explaining plan options to employees.

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