FSA vs HSA Comparison Calculator

Most FSA plans require unused contributions to be spent by the end of the plan year — sometimes with a small grace period or limited carryover — or the money is forfeited back to the employer. HSAs have no such deadline: any unspent balance simply stays in the account indefinitely, which is the core structural reason this calculator only tracks a forfeiture risk on the FSA side.

The same entered contribution amount is checked independently against each account type's own statutory annual limit — the FSA limit and the HSA individual limit are set separately and typically differ from one another. If your entered contribution exceeds one limit but not the other, that side's calculation is capped down while the other side uses the full amount.

No — HSA Annual Tax Savings applies to your entire contribution regardless of whether that money is later spent on qualified medical expenses or left invested to grow, since the tax advantage comes from the contribution itself being pre-tax. An FSA only risks losing the tax-advantaged status of the unspent portion specifically, through forfeiture, not the tax savings already realized on the whole contribution.

It compounds annually on whatever balance accumulates, so its effect grows substantially the longer Years to Project runs — a modest rate difference produces a small gap after just a few years but a much larger one over one or two decades. Someone projecting an HSA balance for retirement decades away should treat the investment return assumption as one of the most consequential inputs in the whole comparison.