Savings Interest Calculator
See how much a certificate of deposit, fixed-term deposit or regular monthly savings plan earns by maturity, with simple or monthly compound interest and an optional tax rate on the interest. Works in any currency.
Enter the amount, term and rate, then press Calculate.
Amounts are rounded down to the cent. Your bank may calculate interest daily or credit it on different dates, so its figure can differ slightly.
How the interest is calculated
With an annual rate r and a term of n months:
| Account | Simple interest | Compounded monthly |
|---|---|---|
| Lump-sum deposit | P × r × n ÷ 12 | P × ((1 + r/12)n − 1) |
| Monthly savings plan | M × r/12 × n(n + 1)/2 | Σ M × ((1 + r/12)k − 1), k = 1 … n |
Monthly contributions are assumed to be made at the start of each month, so the first one earns interest for n months and the last one for one month.
Example: 10,000 deposited for 12 months at 4.5%
Simple interest earns 450.00. Compounded monthly it earns 459.39, which is why a 4.5% rate compounded monthly is quoted as an APY (annual percentage yield) of about 4.59%. With a 24% tax on interest, the simple-interest result drops to 342.00 after tax.
Why a monthly plan earns less than the headline rate suggests
Saving 500 a month for 12 months at 4% simple interest puts in 6,000 but earns only 130.00, not 240.00 (4% of 6,000), because each deposit is in the account for less than a year. On average the money is invested for about half the term.
APR, APY and compounding
- Nominal rate (APR) is the annual rate before compounding. This calculator expects this rate.
- APY / AER / effective rate already includes compounding. If your bank quotes APY, choose simple interest for a 12-month term to get roughly the same result, or convert APY back to a nominal monthly-compounded rate with 12 × ((1 + APY)1/12 − 1).
- The longer the term and the higher the rate, the bigger the gap. 10,000 for 5 years at 4% earns 2,000.00 simple, but 2,209.96 compounded monthly.
Tax on interest
Interest is taxable income in many countries, but the rules vary widely: in the US it is taxed at your ordinary income tax rate; the UK has a personal savings allowance before tax applies; some countries withhold a flat rate at the bank; and tax-advantaged accounts (such as IRAs, ISAs or TFSAs) may be tax-free.
Choose No tax for a tax-free account or to see the gross figure, or Custom tax rate and enter the rate that applies to you. The calculator applies that single rate to the whole interest amount; it does not model allowances, brackets or state and local taxes.
Frequently asked questions
Which currency does it use?
Any. Enter amounts in your own currency; the results are in the same currency, to two decimal places.
What if I withdraw early?
Term deposits and CDs usually charge an early withdrawal penalty, often a few months of interest. This calculator assumes you keep the money until maturity.
Is inflation included?
No. To estimate the real return, subtract the expected inflation rate from the after-tax rate. Borrowing instead of saving? Compare repayment options with the loan calculator.