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Investment Tools

Compound Interest Calculator

Calculate how your capital may grow over time when returns are reinvested monthly. Use this compound interest calculator to estimate future value based on starting capital, monthly return, investment period, and optional monthly contributions.

Calculate compound growthRead the compound interest guide

Quick example

Starting capital

$1,000

Hypothetical monthly return

5%

Estimated value after 24 months

$3,225

This example assumes no monthly contributions and monthly reinvestment of returns.

Compound Growth Calculator

Estimate future value with monthly compounding.

Results are hypothetical and assume a constant monthly return. Real markets do not produce fixed returns every month.

Calculation result

Compound growth summary

Enter your investment assumptions and click calculate to see the estimated future value and total profit.

Updated June 2026

Compound Interest and Investment Growth Guide

Compound interest is one of the most important concepts in long-term investing because returns are reinvested instead of being separated from the original capital. Over time, previous gains can start generating additional gains, which may accelerate portfolio growth.

How compound interest is calculated

Future Value = Principal × (1 + Return Rate) ^ Number of Periods
With monthly contributions, this calculator adds the contribution before applying the monthly return.

This calculator compounds growth monthly. It starts with the opening balance, adds any monthly contribution, applies the monthly return, and then uses the ending balance as the next month’s starting value.

Definition

What is compound interest?

Compound interest means that previous gains are reinvested with the original capital, allowing both the initial investment and accumulated returns to generate future returns.

Investing

Why time matters

The longer money stays invested, the more time compounding has to work. Growth may feel slow at first, but it can become more powerful as profits accumulate and the base capital becomes larger.

Important

Are returns fixed?

No. Financial markets do not produce fixed monthly returns. Use this calculator as a planning and scenario-modelling tool, not as a guarantee of future investment performance.

Compound growth examples

The table below shows how $1,000 could grow when hypothetical monthly returns are reinvested without additional contributions.

Starting capital
$1,000
Return
3%
12 months
$1,425
24 months
$2,032
Starting capital
$1,000
Return
5%
12 months
$1,796
24 months
$3,225
Starting capital
$1,000
Return
10%
12 months
$3,138
24 months
$9,850

Simple interest vs compound interest

Simple interest calculates returns only on the original capital. Compound interest calculates returns on both the original capital and the previous accumulated returns, which can create faster growth over time.

For long-term investing, the difference can become significant, especially when monthly contributions are added consistently and returns are reinvested instead of withdrawn.

Can traders use this calculator?

Yes. It can be used to model trading account growth, but trading returns are not stable or guaranteed. The monthly return field is a mathematical assumption, not a reliable forecast.

Common compound growth mistakes

⚠
Assuming the same monthly return will repeat every month.
⚠
Using unrealistic return expectations when planning.
⚠
Ignoring fees, commissions, taxes, and withdrawals.
⚠
Withdrawing profits instead of reinvesting them.
⚠
Treating calculator projections as guaranteed outcomes.
⚠
Ignoring losing periods or market drawdowns.

Tips for using compound interest wisely

✓
Start early to give compounding more time to work.
✓
Reinvest returns instead of withdrawing them frequently.
✓
Add regular monthly contributions when possible.
✓
Use realistic return assumptions for planning.
✓
Separate mathematical projections from guaranteed results.
✓
Review growth together with risk, volatility, and drawdown.

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Compound Interest Calculator FAQ

What is a compound interest calculator?

A compound interest calculator estimates how capital may grow when returns are reinvested over time, with or without monthly contributions.

How is compound interest calculated?

Compound interest is calculated by applying returns to the current balance, then adding those returns back into the balance for the next period.

Can this calculator be used for trading accounts?

Yes. It can model trading account growth, but trading returns are not fixed or guaranteed.

What is the difference between simple and compound interest?

Simple interest calculates returns only on the original capital, while compound interest calculates returns on both the capital and previous gains.

Do monthly contributions affect the final result?

Yes. Regular monthly contributions can significantly increase the final balance over time when combined with compounding.

Are the results guaranteed?

No. The results are estimates based on fixed-return assumptions. Real investments can rise, fall, or produce uneven returns.