# Compound Interest Calculator

- **URL:** https://codeasystem.com/calculators/finance/compound-interest-calculator/
- **Category:** finance
- **Description:** See how savings grow with compound interest, including optional monthly contributions and any compounding frequency.
- **Primary output:** Future value: $54,713.58

## Inputs
- Starting amount (name: `principal`, type: number, prefix: $, example: 10000)
- Monthly contribution (name: `contribution`, type: number, prefix: $, example: 200)
- Annual return (name: `rate`, type: number, example: 7)
- Time (name: `years`, type: number, example: 10)
- Compounding frequency (name: `compounding`, type: select)

## Outputs
- Future value: $54,713.58
- Total you put in: $34,000.00
- Interest earned: $20,713.58
- Growth multiple: 1.61×

## Formula / methodology
```
FV = P(1 + r/m)^(mt) + C · ((1 + i)^(12t) − 1) / i
i = effective monthly rate from (1 + r/m)^(m/12) − 1
```

The starting balance grows at the periodic rate r/m for t years. Monthly contributions are treated as end-of-month deposits earning the equivalent effective monthly rate, so results stay consistent no matter which compounding frequency you pick.

## Assumptions & limitations
- Constant average return; markets rarely move in a straight line.
- Contributions happen at the end of each month and never change.
- No taxes, fees or inflation are deducted.

## Example
$10,000 growing at 7% a year with $200 added monthly becomes $54,713.58 after 10 years; $34,000 contributed and $20,713.58 earned as growth.

Result for these inputs:

```
Future value: $54,713.58
```

## About this calculator
### Why compounding feels magical

Each period earns returns not just on your money but on all previous returns. Over decades, the interest column dwarfs the contributions column; which is why starting early beats starting bigger.

### The rule that matters most: time

Doubling your time horizon matters far more than chasing an extra percent of return. Run the same inputs at 10, 20 and 30 years to feel the curve bend upward.

## FAQs
### What compounding frequency should I pick?

Match reality: savings accounts usually compound daily or monthly, CDs quarterly or semi-annually, and index funds effectively grow continuously. Differences are small at typical rates.

### Are contributions included in the growth?

Yes; every contribution starts compounding from the month it is deposited.

### Does this account for inflation?

No. Subtract expected inflation from your return rate for a real-terms estimate, or use the inflation calculator separately.

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- [CAGR Calculator](https://codeasystem.com/calculators/finance/cagr-calculator/)

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Last updated: 2026-08-23 · Version: 1.0.0 · [HTML version](https://codeasystem.com/calculators/finance/compound-interest-calculator/)