Compound Interest Calculator
Compound interest means each period's return is earned on a growing balance, including prior gains, so the curve bends upward the longer it runs. Enter a starting balance, a return per trade, month or year, and how many periods to project, and this calculator shows the final value, the total gain, and how long the balance takes to double.
At 2% per month, the balance doubles in about 35 months (exact math), close to the Rule of 72 estimate of 36 months.
Continue with your own chart. Upload a screenshot first, then choose Pro or Elite before Lynx runs the analysis.| month | Balance | Cumulative gain |
|---|---|---|
| 1 | $10,200 | $200 |
| 2 | $10,404 | $404 |
| 3 | $10,612.08 | $612.08 |
| 4 | $10,824.32 | $824.32 |
| 5 | $11,040.81 | $1,040.81 |
| 6 | $11,261.62 | $1,261.62 |
| 7 | $11,486.86 | $1,486.86 |
| 8 | $11,716.59 | $1,716.59 |
| 9 | $11,950.93 | $1,950.93 |
| 10 | $12,189.94 | $2,189.94 |
| 11 | $12,433.74 | $2,433.74 |
| 12 | $12,682.42 | $2,682.42 |
The numbers are only as good as the levels you typed. Upload a chart screenshot and Lynx AI reads the structure for you, so the levels come off the chart instead of a guess.
See an AI chart readHow to calculate compound growth
Each period, the balance is multiplied by (1 + the return per period) and any fixed contribution is added:
Balance after period n = Balance after period n-1 x (1 + r) + contribution
Run that forward for every period and the final value reflects compounding on compounding, not just the sum of each period's gain on the original principal.
Worked example
A $10,000 account earning 2% per month for 12 months, with no added contributions:
- Final value = $10,000 x 1.02^12 = $12,682.42
- Total gain = $12,682.42 - $10,000 = $2,682.42
- That is more than 12 x 2% = 24% simple growth, because months 2 through 12 also compound on the prior months' gains
Per trade vs per month and the Rule of 72
The same math applies whether the period is a single trade, a month, or a year; only the number of periods and the rate per period change. A strategy that nets 10% per trade over 20 trades grows $10,000 to about $67,275, purely from compounding on each trade's result, before any deposits.
The Rule of 72 estimates the same doubling time as 72 divided by the rate per period. At 2% per month, the Rule of 72 gives 72 / 2 = 36 months, close to the exact answer of about 35 months from ln(2) / ln(1.02). The shortcut is most accurate in the 6% to 10% range and drifts further from exact at very high or very low rates.
When it misleads you
This projection assumes a constant return every single period, which no real trading account delivers; a sequence with the same average return but real drawdowns compounds to a lower final value than a smooth path, because losses shrink the base that later gains compound on. See compound interest in trading for how volatility drags down compounded returns, and the drawdown recovery calculator for what a loss actually costs you before you can compound again.
How to use this tool
- Choose your period. Select per trade, per month or per year to match how you think about your return.
- Enter your starting balance. Type the account balance you are projecting from.
- Enter your return per period. Type your average return per period as a percentage. It can be negative.
- Enter the number of periods. Type how many periods to project forward, and an optional fixed contribution per period.
- Read the projection. The tool shows the final value, total gain, doubling time, and a period-by-period table.
Frequently asked questions
What is a trading compound interest calculator?
It projects how a starting balance grows when a return per period is reinvested each period, optionally with a fixed contribution added each period. Because each period compounds on the prior balance, including reinvested gains, the growth curve bends upward the longer it runs.
What is the compound interest formula?
A = P(1 + r)^t for a single compounding rate applied t times, where P is the principal and r is the rate per period as a decimal. This calculator runs the period-by-period version so it can also add a contribution each period, which the closed-form formula alone cannot do.
What is the Rule of 72 and how does it compare here?
The Rule of 72 estimates doubling time as 72 divided by the percentage rate per period. This calculator also computes the exact doubling time using ln(2) / ln(1 + r), so you can see how close the shortcut is at your specific rate.
Does this account for losing periods?
Yes, a negative return per period is a valid input and compounds the same way a positive one does, reducing the balance each period. This is also why drawdowns hurt compounding more than an equivalent gain helps it; see the drawdown recovery calculator for that math.
Is this compound interest calculator free?
Yes. It runs entirely in your browser, requires no signup, and nothing you enter is sent anywhere.
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Educational only. Not financial advice. NFA. Bullynx is not a registered investment adviser or broker-dealer. Trading and investing involve significant risk of loss. Read the full risk disclosure.