A compound interest calculator grows a balance forward. You give a principal, a nominal annual rate, a compounding frequency, and a whole number of those periods. You may also give a level contribution deposited at the end of each period. The page returns the future value, the total deposited, the interest, and a plain description of the term, such as “24 monthly periods is 2 years.”
This is not a loan payment. A loan payment calculator takes a balance down with a fixed installment. This page does the opposite direction: money put in, then a future value. When both pages are published, the Loan Payment Calculator is the neighboring tool, and the two formulas should not be swapped.
The rate is whatever you type. The page does not fetch a savings rate, add inflation, subtract tax, or suggest that a result is a good investment. Daily compounding uses a 365-day year. It does not walk calendar dates, and it does not know about leap days.
Enter in a field runs Calculate. A decimal period is rejected. A blank rate is rejected. A blank contribution is treated as zero.
Let r be the annual rate as a decimal, m the number of compoundings per year, N the number of periods, P the principal, and C the contribution per period. If the rate is 0, future value = P + C × N, added in cents, and the interest is 0. Otherwise i = r ÷ m, and the future value is P × (1 + i)^N plus C × (((1 + i)^N − 1) ÷ i). The contribution term assumes each deposit lands at the end of a compounding period, on the same cadence as the compounding. The future value is then rounded half away from zero to cents. Total deposited is P + C × N in cents. Interest is the rounded future value minus the total deposited.
Annual uses m = 1, quarterly m = 4, monthly m = 12, and daily m = 365. One annual period at 10 percent on 1000 with no contribution is exactly 1100.00, which is the check that the power and the rounding agree on a simple case. A very long daily run can still move by cents relative to a bank’s own rounding. The page says the displayed cents are the rounded formula, not a statement.
Principal 1000, rate 10 percent, annual, 1 period, contribution 0: future value 1100.00, deposited 1000.00, interest 100.00. The term line reads “1 annual period is 1 year.” Principal 1000 and a contribution of 50 each month for 12 months at a 0 rate: future value 1600.00, because 1000 + 50 × 12 uses addition and does not divide by a zero rate. Principal 1000 at 10 percent compounded monthly for 12 periods, with no contribution, finishes a little above 1100 because there are twelve growth steps inside the year. The term line reads “12 monthly periods is 1 year.”
1000 × (1 + 0.10) ^ 1 = 1100.00
Rate 0: 1000 + 50 × 12 = 1600.00The formula runs locally. Principal and contribution amounts are not uploaded and are not stored. Nothing on this page contacts a bank or a rate feed. Clear the fields before you leave a shared computer.
The rate is a nominal annual rate you type. A contribution, if any, is deposited at the end of each compounding period, on the same cadence. Daily uses a 365-day year, not calendar dates. The future value is rounded half away from zero to cents. This is formula rounding, not a bank statement, and not an investment recommendation.
The term line says “24 monthly periods is 2 years.” The count is compounding periods, not a separate month field.
The usual formula divides by the periodic rate. At zero that divisor vanishes, so the page adds the principal and the contributions in cents instead.
No. Daily means a 365-day year. Leap days and calendar dates are outside this page.
No. Interest here is the rounded future value minus what you deposited. It ignores tax, fees, and any rate the bank might actually offer.