Bank Bonus Calculator: Is That Bonus Worth Parking Your Cash?

By Tom, CPA · Updated October 25, 2026

TL;DR: A bank bonus is only as good as what's left after you subtract the interest your cash would have earned elsewhere, any fees, and taxes. Enter the offer terms and your alternative rate to see the true after-tax gain and an annualized return you can compare across offers.

Educational only, not tax, legal, or investment advice. Examples are illustrations, not predictions. Rules and limits change; verify current figures and talk to a qualified professional about your situation.

Bank bonus ads display one number in a large font. The numbers that matter are in a smaller font, or not displayed at all: how much cash you must deposit, how long it must stay, what the account pays in the meantime, and what the IRS will take. This calculator puts all of those in one place.

It's deterministic and runs entirely in your browser; nothing is sent anywhere. For the rules, eligibility traps and tax reporting behind bonuses, read the bank account bonuses guide.

CPA Warning Label: A $400 bonus that costs you $400 of interest is a very elaborate way to fill out forms. Let the math decide.

Inputs

• Bonus amount: the cash bonus promised, before tax.
• Cash you must park: the deposit or balance you must hold to qualify. For a checking bonus that only needs a direct deposit, use the balance you'll actually keep there.
• Days the cash must stay: the holding period from the terms, plus any days of transfer time.
• Rate your cash earns elsewhere: the APY of your current high-yield savings account or money market fund. This is your opportunity cost.
• Rate the bonus account pays: often near zero for checking accounts.
• Combined marginal tax rate: your federal bracket plus state rate. Bonuses are generally taxed as ordinary income, typically reported on Form 1099-INT or sometimes 1099-MISC.
• Fees: monthly maintenance fees you won't avoid, early closure fees, or wire costs.

Opportunity cost of parked cash

Money in a no-interest checking account isn't free. If it would have earned 4% somewhere else, every day it sits in the bonus account costs you. The calculator computes forgone interest as:

deposit × (alternative rate − account rate) × days ÷ 365

This simple-interest approximation is close enough for holding periods under a year. The longer the holding period and the bigger the deposit, the more the bonus gets eaten. Large savings bonuses with six-month holds are where this bites hardest.

Tax rate

The bonus is taxable. But the interest you gave up would also have been taxable, so the tax cost is applied to the difference: (bonus − forgone interest) × tax rate. Fees aren't treated as deductible, which is the usual case for personal accounts.

Early retirees using ACA marketplace coverage should remember that bonuses add to modified adjusted gross income. If you're near a subsidy threshold, the true marginal rate on a bonus can be higher than your bracket; see ACA MAGI management.

Annualized return

Offers have different deposits and durations, so raw dollars don't compare well. The annualized return converts your after-tax gain into an extra yearly return on the parked cash: after-tax gain ÷ deposit × 365 ÷ days. A result of 3% means the bonus added about three percentage points per year on that cash, on top of what it would have earned anyway. Small-deposit checking bonuses can show enormous annualized returns because almost no cash is tied up; that's real, but the dollar gain is capped by the bonus, so also look at the dollar figure.

Example

Illustration (the default inputs, all assumptions): a $400 bonus requires $20,000 held for 90 days in an account paying 0%. Your savings elsewhere earns 4%, and your combined tax rate is 27%.

Now change the holding period to 180 days: forgone interest doubles to about $395, and the gain nearly disappears. Change it instead to a $300 checking bonus needing only $500 parked for 60 days at 22% tax, and the after-tax gain is about $231. That's why small-balance direct deposit bonuses often beat flashy savings bonuses.

Caveats

• The calculator assumes you meet every requirement. Missing one turns the bonus into zero and leaves the costs.
• It ignores your time. If an offer takes three hours and nets $40, decide whether that's a good hourly rate for you.
• Rates can change during the holding period; use your best estimate.
• Keep your emergency fund accessible; don't lock it up to chase a bonus.
• This is an educational estimate, not tax advice.