Quick answer
A high-yield savings calculator shows what a deposit earns at an online-bank APY versus a low branch rate. $15,000 held 3 years grows to $17,164 at 4.5% APY but only $15,457 at 1.0% — a $1,707 difference for the same money and the same federal insurance.
How the High-Yield Savings Calculator works, step by step
Enter your deposit, a monthly contribution, the time period, the high-yield APY and the regular APY. Both accounts use monthly compounding with the same deposit and the same contribution, so the gap between them is pure rate advantage — nothing else differs, and the year-by-year table lists both balances and the gap at each year-end so the cost of waiting is visible rather than abstract.
Adding a monthly contribution widens the gap further, because every deposit earns the higher rate too. With a $10,000 deposit plus $300 a month over 5 years, a 4.5% account reaches $32,662 while a 0.4% account reaches $28,380 — a $4,281 difference on $28,000 paid in. The contribution does not change the rate story; it scales it.
Online banks can pay more because they have no branch network to fund, and they compete nationally for deposits. The accounts carry the same FDIC insurance — up to $250,000 per depositor, per bank — as a branch account. The trade-offs are usually no cash deposits and transfers that take 1 to 3 business days, which matters for money you might need instantly.
Remember the rate is variable. The APY you see today follows the federal funds rate with a lag — the Fed held its target at 3.75% to 4.00% in October 2026 after raising it in September, and top online accounts paid about 4.2% to 4.4% APY in November 2026 against a 0.38% national average. Re-run the calculator when rates move rather than treating the first projection as a forecast.
The projection is pre-tax. Interest is taxed as ordinary income in the year it is paid, so on the $2,164 of interest in the worked example a saver in the 22% bracket owes about $476. That does not change the comparison — both accounts are taxed the same way — but it does change what you keep, and it is one more reason the account suits an emergency fund rather than long-term wealth building. Keep one month of expenses in your everyday account for instant access and the rest here, since transfers out can take a few days.
The formula
Future value = Deposit × (1 + APY/12)^(12t), plus monthly contributions compounded the same way. Interest earned = future value − deposit − total contributions.
Worked example — try it on the calculator above
Worked example: $15,000 for 3 years at 4.5% vs 1.0%
With monthly compounding, $15,000 at 4.5% APY becomes $15,000 × (1 + 0.045/12)^36 = $17,164, so interest is $2,164. At 1.0% the same deposit becomes $15,457, so interest is $457. Same deposit, same insurance, same access — the higher APY pays $1,707 more over the 3 years. At the 0.38% national average the balance would reach only about $15,172, which is why the comparison that matters is against your current account's actual rate, not against 1.0%.
Frequently Asked Questions
Why can online banks pay higher APYs?
They have no branch network to fund, and they compete nationally for deposits. The accounts carry the same FDIC insurance (up to $250,000 per depositor, per bank) as a branch account. The trade-offs are usually no cash deposits and transfers that take 1 to 3 business days.
Is interest from a high-yield savings account taxed?
Yes, as ordinary income in the year it is paid, at your marginal rate. On $2,164 of interest, a saver in the 22% bracket owes about $476. The calculator shows pre-tax growth, so subtract your tax rate from the interest figure to see what you keep.
How many withdrawals can I make each month?
Federal rules that once capped savings withdrawals at six per month were suspended in 2020, but many banks keep their own limits or excess-withdrawal fees in the account terms. Check the fee schedule if you plan to use the account like a current account.
Should my emergency fund sit in a high-yield account?
Yes — it is the standard place for one. The money stays liquid and insured while earning a market rate. Keep one month of expenses in your everyday account for instant access and the rest in the high-yield account, since transfers out can take a few days.
Estimates, not advice. This calculator provides educational estimates based on the inputs you enter and the assumptions shown on this page. It is not financial, tax or investment advice, and it cannot see your full situation. Verify important figures against official sources, and consider a qualified professional for decisions about your own money. See our Disclaimer and Methodology.