Calculate interest using a clear, flat-rate formula. Estimate interest earned on savings or the total interest charged on a simple-interest loan, then compare with annual compounding.
Savings and borrowing modes • Optional tax and fees • Results calculated in your browserSimple interest accumulation schedule
| Period | Interest this period | Cumulative interest | Balance |
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Full years are shown separately. A final partial year is included when applicable.
How simple interest is calculated
Simple interest is calculated on the original principal rather than on previously accumulated interest. This calculator can solve for the ending amount, starting principal, annual rate, or required time. It also provides an annual accumulation schedule and optional savings-tax and fee assumptions.
View the formulas
Simple interest is I = P × r × t, where P is principal, r is the annual rate as a decimal, and t is time in years. The basic amount is A = P(1 + rt). Rearranging gives P = A ÷ (1 + rt), r = (A ÷ P − 1) ÷ t, and t = (A ÷ P − 1) ÷ r.
For months, time in years is months divided by 12. For days, it is days divided by the selected 360- or 365-day basis. Optional tax reduces savings interest only; a fee reduces savings proceeds or increases borrowing cost.
If selected, annual compounding is compared using P × (1 + r)t. It is an illustration, not a prediction.
Example: simple interest on $10,000
At a 6% annual simple interest rate for three years, interest is $10,000 × 0.06 × 3 = $1,800 and the amount before fees or tax is $11,800. The same relationship can be rearranged to recover the principal, rate, or term.
Savings or borrowing
Savings mode shows gross interest, optional estimated withholding, net interest, and the amount after a one-time fee. Loan mode shows flat simple interest and total repayment; tax is not applied to borrowing. Real lender amortization, APR, payment timing, and fees may differ.
Simple interest compared with compound interest
Simple interest always uses the original principal. Compound interest adds earned interest to the balance, so later interest may be earned on earlier interest. The optional comparison uses the same principal, rate, and time.
Questions and limitations
Why can a lender’s number differ?
A contract may use exact dates, daily balances, payment timing, fees, APR, or a reducing-balance method. This tool applies flat simple interest to the original principal.
Does this calculate APR or tax liability?
No. It does not calculate APR or determine tax liability. Any tax percentage is only a user-entered savings illustration.
Does the currency selector convert money?
No. It changes formatting only.
Are my inputs stored?
The calculation runs in your browser. The website or installed plugins may have separate analytics and privacy practices.
Results are estimates for general information and are not financial, tax, or lending advice.