Calculated the way banks really do it: interest on your daily balance, credited monthly - not an investment-style annual growth rate. Model a bonus rate that reverts to an ongoing rate, since that is how most high-interest savings accounts are actually structured.
Real savings accounts do not compound to a target annual figure the way an investment return does. Banks calculate interest daily on your closing balance - daily interest = balance × (annual rate ÷ 365) - then credit the accumulated amount to your account, usually monthly. Because that credited interest then earns interest itself the following month, the account effectively compounds monthly as a side effect, not because the bank applied a monthly-compounding formula directly.
That distinction matters: it means the rate printed on your account (the nominal rate) and what you actually earn over a year (the effective annual yield) are not quite the same number - the effective yield ends up very slightly higher, purely from that monthly reinvestment. This calculator applies the nominal rate you enter using the real daily-accrual method, the same way the numbers on your actual statement would be worked out.
Both tools show a balance growing over time, which can make them look interchangeable. They are not modelling the same thing. A savings account is a bank deposit with a rate that is fixed or variable but always known in advance, calculated daily, and usually accessible whenever you want it. Money in shares, a managed fund, or a retirement account is market-linked - the return is not a quoted rate but a long-run average of gains that vary year to year, often locked away for decades, which is why inflation and multi-decade staging matter there in a way they don't for a one-to-five-year savings goal.
Use this page for a bank account, an emergency fund, or a house deposit - somewhere you can name the actual interest rate. Use the retirement calculator for market-linked, multi-decade growth, career-break stages, and what the balance is really worth after inflation - a genuinely different set of questions.