Compound interest and future value calculator

The deposit grows at the effective rate for each contribution period, and each contribution grows from the date it is paid in.

FV = P(1 + i)^n + C × ((1 + i)^n − 1) / i × (1 + i·t)
i = (1 + r/m)^(m/f) − 1, or e^(r/f) − 1 for continuous compounding
n = years × f contributions; t = 1 for contributions at the start of each period, else 0

Assumptions and limits

• The rate stays the same throughout. Tax, fees and inflation are not deducted.
• Years × contributions per year must be a whole number of periods.
• An educational calculation, not financial, tax, legal or investment advice.

Worked example

10,000 at 5% compounded monthly for 10 years grows to 16,470.09. Adding 100 at the end of each month brings it to 31,998.32. The same growth is what spreadsheet FV returns: FV(5%/12, 120, −100, −10000) = 31,998.32.

References

• Microsoft Excel: FV function
• U.S. SEC Investor.gov: compound interest calculator and explanation