# Compound Interest Calculator: See Your Savings Grow

See how savings grow with compound interest: starting sum, monthly contributions, rate and compounding frequency, with a yearly chart. Includes a CAGR calculator.

Interactive tool: https://lookup.sg/tools/compound-interest-calculator

## How this works
Compound interest pays interest on your interest. Each period the balance grows by the annual rate divided by the number of compounding periods a year, so S$10,000 at 5% compounded monthly becomes S$10,000 × (1 + 0.05/12)^120 = S$16,470 after 10 years, against S$15,000 with simple interest.

Monthly contributions are added at the end of each month and then compound along with the rest. When interest compounds less or more often than monthly (yearly, quarterly, daily), the calculator converts the rate to the equivalent monthly growth, so the effective annual rate shown is what the balance actually grows by in a year.

The CAGR tab works backwards: compound annual growth rate = (ending value ÷ starting value)^(1 ÷ years) − 1. It is the single steady rate that would have produced the same result, which makes investments over different periods comparable.

The rate is an assumption you set. Fixed deposits and savings accounts pay a quoted rate; investment returns vary year to year and are not guaranteed. Figures are before fees, tax and inflation.

## FAQs
### How much will S$10,000 grow to at 5% compound interest over 10 years?
S$10,000 at 5% a year compounded monthly grows to about S$16,470 after 10 years, or S$16,289 if interest compounds once a year. Simple interest at the same rate would give S$15,000.

### How much will I have if I save S$500 a month for 20 years?
Saving S$500 a month for 20 years puts in S$120,000. At 4% a year compounded monthly it grows to about S$183,400; at 6% it grows to about S$231,000. The difference is entirely compound interest.

### Does compounding frequency make a big difference?
Less than most people expect. S$100,000 at 3% for one year earns S$3,042 compounded monthly and S$3,045 compounded daily. The rate and the number of years matter far more than how often interest is added.

### How do I calculate CAGR?
Divide the ending value by the starting value, raise it to the power of 1 ÷ years, and subtract 1. An investment that grew from S$10,000 to S$18,000 in 5 years has a CAGR of about 12.47% a year.

### What is the rule of 72?
Divide 72 by the annual rate to estimate how many years money takes to double. At 6% that is about 12 years; the calculator shows the exact doubling time for the rate you enter.

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