# Compound interest calculator

Written on 4 November 2026 by Ratio. Every example was run through Ratio that day.

Write the sum, the rate and the time, and say how often interest is added. Ratio shows what it grows to, and you can change any number to see what moves.

## How often it compounds

| 10k at 4% for 5 years | 12,166.53 |
| --- | --- |
| 10k at 4% for 5 years compounded quarterly | 12,201.9 |
| 10k at 4% for 5 years compounded monthly | 12,209.97 |
| 10k at 4% for 5 years compounded daily | 12,213.89 |

Without “compounded”, interest is added once a year. The more often it is added, the sooner interest earns interest of its own.

## Adding every month

| save 500/month at 7% for 20 years | 260,463.33 |
| --- | --- |
| (10000 at 7% for 20 years compounded monthly) + (save 500/month at 7% for 20 years) | 300,850.72 |

For goals, inflation and retirement numbers, see the [investment calculator](https://useratio.app/investment-calculator).

## Growth rate from two values

| cagr(1000, 2500, 5 years) | 20.11% |
| --- | --- |

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## Questions

**What is compound interest?** Interest that is added to the balance, so the next period's interest is worked out on a larger sum. Simple interest is only ever paid on the starting amount.

**What is the formula?** Final amount = start × (1 + rate ÷ n)^(n × years), where n is how many times a year interest is added.

**What is the effective yearly rate?** What the rate comes to over a whole year once compounding is counted. 4% compounded monthly is 4.07% a year.

Source: https://useratio.app/compound-interest-calculator