Compound Calculator [Free Tool]
See how reinvested returns grow an account over time — and why time matters more than the rate. Project your balance from a starting amount, a periodic return, and a horizon.
Disclaimer: Trading financial instruments involves risk, and everything on this page is provided for educational purposes only. Nothing here is financial advice or a recommendation to buy or sell any instrument.
Final Balance
$16288.95
Total Contributions
$0.00
Total Profit
$6288.95
How is this calculated?
Final = Starting × (1 + rate)^periods + Σ contributions × (1 + rate)^remaining
Read the full user guide
Every parameter, formula, and worked example — a complete reference for this tool.
What is compound interest, and how does it grow an account?
Compound interest is what happens when your returns stay in the account and start earning returns of their own. For a trader, that means each profitable period grows the base that the next period builds on, so growth accelerates over time instead of moving in a straight line. The compound interest calculator turns three inputs — starting balance, periodic return, and number of periods — into a projected growth curve, so you can see what reinvesting actually does over the long run.
Key concepts
Compounding
Each period's return is added to the balance, so the next period earns on a larger base — the classic 'interest on interest' effect.
Periodic return
The gain per period, expressed as a percentage. A fixed return is an idealized assumption; real trading returns vary and can turn negative.
Withdraw vs. reinvest
Whether you take each period's profit out changes the long-term result dramatically. Compounding only works when returns stay in the account.
A worked example with real numbers
- 1
Enter the starting balance and return
You start with $5,000 and earn 3% per month.
- 2
Choose the horizon
Over 24 months, reinvesting every gain.
- 3
Compute the future value
Future value = $5,000 × (1.03)^24 ≈ $5,000 × 2.03 ≈ $10,160.
- 4
Compare with simple growth
Without reinvestment the gains would be $3,600, ending around $8,600. Compounding added roughly $1,560 — the 'interest on interest' effect.
How to use it
Enter the starting balance
The account balance you are beginning the projection with.
Enter the periodic return and number of periods
For example, 2% per period over 12 periods.
Choose whether to reinvest
Decide if each period's gain is added back into the base.
Read the final balance and growth curve
Compare how compounding diverges from simple, non-reinvested growth over time.
The formula, step by step
Compound future value
Future value = Starting balance × (1 + periodic return)^periods
Assumes a constant periodic return with all gains reinvested.
Mistakes traders make
✗ Projecting a fixed positive return as if losses never happen
✓Real returns swing and turn negative. The model is for understanding the mechanism, not for forecasting the balance.
✗ Choosing the period and return on mismatched time scales
✓A 3% monthly return over 24 years is meaningless. Match the period to the return's time frame.
✗ Forgetting that compounding amplifies losses too
✓The same curve that accelerates gains accelerates repeated losses downward. It works on whatever return you actually get.
When this tool fits — and when it does not
Use it when
- ✓Projecting how reinvested returns grow an account over many periods.
- ✓Comparing compound growth against withdrawing gains each period.
- ✓Building intuition for why time matters more than the rate.
Skip it when
- ✗Forecasting a real account balance from an idealized fixed return.
- ✗Using a period that does not match the return's frequency.
- ✗Treating the projection as a promise of future performance.
Practical tips that actually help
Use conservative return assumptions
Run the projection at a pessimistic rate too. If the plan still works there, it is worth pursuing.
Let the curve teach the lesson
The bend in the curve — growth accelerating on itself — is why starting early and staying invested beats chasing a higher rate.
Reinvest as the default
The biggest compounding lever is keeping gains in the account. Withdrawal is the enemy of the curve.
Related & next steps
Frequently asked questions
How is a compound calculator different from CAGR?▾
A compound calculator projects forward: you input a periodic return and watch the balance grow. CAGR works backwards from historical start and end values, smoothing a period's total gain into an annualized rate. One predicts, the other summarizes.
Why does real trading compound less cleanly than the model?▾
The model assumes the same positive return every period. Real trading has winners and losers and drawdowns, and a negative period shrinks the base that future growth depends on. Use the result to understand the mechanism, not to forecast returns.
How do I choose the period?▾
Match the period to your return's time frame: if your return is monthly, use months; if annual, use years. Keeping the return and the period consistent is what makes the projection meaningful.
What happens if I set the return to zero?▾
With a zero return, the balance stays flat no matter how many periods you add — a useful reminder that compounding needs a positive return to do anything at all.
Can compounding work against me?▾
Yes, and it is worth understanding. Compounding amplifies whatever return you actually get, so repeated losses compound the damage to your balance just as surely as gains compound the growth.
Why does the curve bend upward instead of rising in a straight line?▾
Because each period earns on a larger base than the last. The difference between compounding and simple growth starts small and widens dramatically over many periods, which is why time is the most important input.
Ready to validate your first strategy?
Put someone else's strategy — or your own idea — through the real data. Free to start, no card required.
No credit card required · 50 free credits on signup
This page is based on the standard compound interest formula from general financial mathematics and is provided for educational purposes only.
Disclaimer: The tools and content on this site are provided for educational purposes only and do not constitute investment advice. Trading and investing involve a substantial risk of loss, and past performance does not guarantee future results.