Compound Interest Calculator

First, select the quantity to be solved for, any one of Future value, Present value, interest rate, or time, then set values for the other three parameters by using the sliders or by typing decimal numbers into the text fields.

Next, choose a compounding frequency. Finally, click the button to compute the unknown value.

The interest rate should be converted from a percent and entered as a decimal number.

The time parameter should be in years, so months, days, and weeks should be converted to years by dividing by 12, 52, or 365 respectively; for instance,

3 years + 8 months = 3 years + 8/12 years = 3 years + 0.66667 years = 3.66667 years

6 weeks + 5 days = 6/52 years + 5/365 years = 0.11538 years + 0.01370 years = 0.12908 years

Exploration 1:
The time values are plotted along the horizontal axis; the Future values, against the vertical axis. The Present value also appears in the graph, although not as one of the coordinate axes. How does the Present value appear?

Exploration 2:
A certain savings account earns interest at a fixed rate over a predetermined period of time with only a single initial deposit. Which compounding frequency returns the greatest interest?

Exploration 3:
Maxwell Moneybags makes a large long-term investment. Peter Pennypincher makes a smaller investment at the same interest rate and compounding frequency. Whose investment doubles first?