# Compound Interest Calculator

URL: https://speedycalculator.com/calculators/finance/compound-interest/
Last updated: 2026-10-25

> The compound interest calculator works out the future balance of savings or an investment with compound interest – any compounding frequency from yearly to continuous, plus regular deposits or withdrawals made at the start or end of each period.

## Inputs

- Initial balance
- Annual interest rate (%)
- Term (years, months)
- Compounding frequency
- Additional deposit (negative for withdrawal)
- Deposit frequency
- Deposit timing

## Results

- Final balance
- Total principal (initial + deposits)
- Total compound interest
- Effective annual rate (APY)
- Interest with simple interest (initial balance only)

## Formula

```
A = P(1 + r/n)^(nt) + PMT × [(1 + i)^N − 1] ÷ i × (1 + i × timing)
i = interest rate per deposit period; N = number of deposits
```

## Explanation

Compound interest earns interest on interest. With regular deposits, a modest monthly amount grows into a large sum: $200 a month at 5% for 30 years becomes about $166,000, of which $94,000 is interest.

### How to use the Compound Interest Calculator

- **Initial balance**
- **Annual interest rate**
- **Term**
- **Compounding frequency**
- **Additional deposit (negative for withdrawal)**
- **Deposit frequency**
- **Deposit timing**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the initial balance, interest rate, term and compounding frequency, plus any regular deposit (or a negative amount for withdrawals) with its frequency and timing.

### Tips

- Use the nominal annual rate and pick the compounding frequency your bank or broker states.
- Small differences in return or fees compound into large differences over decades.
- Run the calculation with a cautious, a central and an optimistic return to see the range of outcomes.
- Past returns do not guarantee future returns – nothing here is investment advice.

### Common mistakes to avoid

- Comparing an APR with an APY or effective rate.
- Ignoring inflation, taxes and fees when judging a real return.
- Entering a percentage as a decimal (5 instead of 0.05 is correct here).

### Inputs explained

FieldWhat to enterInitial balanceAmount in your currencyAnnual interest rateIn %TermUnits: years, monthsCompounding frequencyChoose one: Yearly, Semi-annually, Quarterly, Monthly …Additional deposit (negative for withdrawal)Amount in your currencyDeposit frequencyChoose one: Monthly, Bi-weekly, Weekly, Quarterly …Deposit timingChoose one: End of each period, Beginning of each period

### What each result means

- **Total compound interest** = [Final balance] - [Total principal (initial + deposits)]
- **Effective annual rate (APY)** = effr([Annual interest rate]÷100, [Compounding frequency])×100
- **Interest with simple interest (initial balance only)** = [Initial balance]×[Annual interest rate]÷100×[Term]

### Example values

How the main result changes when **Initial balance** changes and everything else stays at the example values above:

Initial balanceFinal balance2,50019,710.453,75021,769.215,00023,827.986,25025,886.747,50027,945.510,00032,063.02

## Worked example

Inputs — Initial balance: $5,000; Annual interest rate: 5 %; Term: 10 years; Compounding frequency: Monthly; Additional deposit (negative for withdrawal): $100; Deposit frequency: Monthly; Deposit timing: Beginning of each period.

Results — **Final balance = $23,827.98**; Total principal (initial + deposits) = $17,000.00; Total compound interest = $6,827.98; Effective annual rate (APY) = 5.116 %; Interest with simple interest (initial balance only) = $2,500.00.

## FAQ

**What is the compound interest formula?**
A = P(1 + r/n)^(nt), plus the future value of any regular deposits.

**How often should interest compound?**
More often is better for savers, but the difference between monthly and daily is small.

**What is the rule of 72?**
Divide 72 by the interest rate to estimate the years to double your money.

**What formula does the Compound Interest Calculator use?**
A = P(1 + r/n)^(nt) + PMT × [(1 + i)^N − 1] ÷ i × (1 + i × timing).


## Sources

- [U.S. SEC – Investor.gov compound interest and investing basics](https://www.investor.gov/)