High-Yield Savings APY Calculator
Compare two savings accounts using the same deposits and timeline. See how promotional rates and monthly fees change your interest and ending balance.
Side-by-side account results
| Measure | Account A | Account B |
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Annualized return after fees uses the timing of your contributions and the final balance. It is not the bank's advertised APY. N/A means these cash flows do not produce a meaningful annualized return, including when no money is invested for a positive period.
Savings milestones
| Month | Total contributed | Account A balance | Account B balance |
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APY, interest rate and compounding
Annual percentage yield (APY) includes the effect of compounding. A nominal annual interest rate does not. For a nominal decimal rate r compounded n times per year, APY = (1 + r/n)^n − 1. For a known decimal APY a, the equivalent nominal rate is r = n × ((1+a)^(1/n) − 1).
For example, 5% nominal interest compounded monthly produces about 5.1162% APY. If an account already quotes 5% APY, that yield must not be compounded a second time. Changing frequency while holding APY fixed changes the equivalent nominal rate, not the effective annual growth.
Monthly deposits and promotional expiration
The projection uses equal monthly periods, with an equivalent monthly growth rate i = (1+APY)^(1/12) − 1. A beginning-of-month deposit earns that month's interest; an end-of-month deposit does not. The opening balance and the first beginning-of-month deposit both enter at time zero. There are exactly as many recurring deposits as months in the savings period.
A promotion lasting 3 months applies in months 1, 2 and 3; the standard rate applies from month 4. If the promotion lasts beyond the projection, the standard rate is not used. A promotional APY is an annualized rate, not a promise to earn that percentage during a short promotion.
This equal-month estimate includes accrued growth between compounding dates. It does not reproduce a bank's daily balance, calendar-day, interest-crediting or cent-rounding rules. Frequency is used to convert nominal rates to APY; the simulation is not a ledger of discrete bank interest payments.
Fees and effective return
Ending balance = opening balance + recurring deposits + interest earned − account fees. Fees are paid at each month-end, reducing the balance available to earn future interest. If an account cannot cover a fee, the calculator stops and identifies the month; it does not assume an overdraft or waive unpaid fees.
Net growth is interest earned minus fees. The annualized return after fees is a money-weighted internal rate of return: the constant monthly return that would turn your opening balance and timed deposits into the final balance, converted to an annual rate using (1+monthly return)^12 − 1. Unlike net growth divided by total contributions, this accounts for how long each deposit was invested. It can be negative even when the quoted APY is positive. Very short periods can produce large annualized losses.
Why might a higher APY account finish with less money?
A short promotional period, a lower subsequent rate or higher fees can outweigh an initially higher APY. Compare the full period using the same deposit schedule. Check each provider's terms separately for rate tiers, minimum balances, fee waivers and eligibility.
What does N/A mean for annualized return?
A return cannot be inferred when no money was invested before the final valuation, or when the final balance is less than a simultaneous end-of-month deposit. A zero terminal value on earlier invested funds is shown as a 100% loss. The dollar balances and fees remain the primary comparison.
Source: the CFPB definition of annual percentage yield explains that APY reflects interest and compounding. Our deposit-and-fee projection is a planning model, not a regulatory APY disclosure calculation.