compound-interest-calculator.app

Compound Interest Calculator

Compound interest is interest calculated on your initial deposit plus all previously earned interest. Because each period's interest is added to the balance before the next calculation, your money grows exponentially rather than linearly.

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  • Private

    Your data stays on your device.

  • Instant Results

    Real-time calculations and graphs
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CompoundFX on iPad and iPhone showing a compound growth projection and saved scenarios

Calculate compound interest

Your Inputs

Monthly contributions compound monthly, so the frequency is locked to monthly while you're contributing.

Results

Year-by-Year Growth Table

Year-by-year growth of $10,000 at 7% with $200 monthly contributions over 30 years
YearStart BalanceContributionsInterestEnd Balance
1$10,000.00$2,400.00$801.42$13,201.42
2$13,201.42$2,400.00$1,032.85$16,634.27
3$16,634.27$2,400.00$1,281.01$20,315.28
4$20,315.28$2,400.00$1,547.11$24,262.39
5$24,262.39$2,400.00$1,832.45$28,494.83
6$28,494.83$2,400.00$2,138.41$33,033.24
7$33,033.24$2,400.00$2,466.49$37,899.74
8$37,899.74$2,400.00$2,818.29$43,118.03
9$43,118.03$2,400.00$3,195.52$48,713.55
10$48,713.55$2,400.00$3,600.02$54,713.58
11$54,713.58$2,400.00$4,033.77$61,147.34
12$61,147.34$2,400.00$4,498.86$68,046.20
13$68,046.20$2,400.00$4,997.58$75,443.79
14$75,443.79$2,400.00$5,532.35$83,376.14
15$83,376.14$2,400.00$6,105.79$91,881.93
16$91,881.93$2,400.00$6,720.67$101,002.60
17$101,002.60$2,400.00$7,380.00$110,782.60
18$110,782.60$2,400.00$8,087.00$121,269.60
19$121,269.60$2,400.00$8,845.11$132,514.70
20$132,514.70$2,400.00$9,658.02$144,572.72
21$144,572.72$2,400.00$10,529.69$157,502.41
22$157,502.41$2,400.00$11,464.38$171,366.79
23$171,366.79$2,400.00$12,466.64$186,233.43
24$186,233.43$2,400.00$13,541.35$202,174.77
25$202,174.77$2,400.00$14,693.75$219,268.52
26$219,268.52$2,400.00$15,929.46$237,597.98
27$237,597.98$2,400.00$17,254.49$257,252.47
28$257,252.47$2,400.00$18,675.32$278,327.79
29$278,327.79$2,400.00$20,198.86$300,926.65
30$300,926.65$2,400.00$21,832.53$325,159.17

Final Balance

$325,159.17

Total Contributions
$82,000.00
Total Interest
$243,159.17
Final Balance
$325,159.17
$0$81K$163K$244K$325K08152330

The Power of CompoundingYou contributed $82,000 but earned $243,159 in interest.

Unlock unlimited scenarios, goal planning, and PDF reports with CompoundFX. Free to download. Optional one-time Pro upgrade. No subscription.

Download CompoundFX on the App Store

100% Free to download. No subscription.

Why Compound Interest Changes Everything

Unlike simple interest, compound interest earns interest on both your initial investment and the interest that accumulates over time — so every year of head start multiplies the end result.

  • Start small and grow big
  • Time is your greatest asset
  • Consistency beats timing
Learn how it works →

The Earlier You Start, The More You Grow

Investing $200/month at 7% until age 65: starting at 25 grows to $524,963 ; starting at 35 grows to $243,994 ; starting at 45 grows to $104,185 .

$0K $131K $262K $394K $525K 25 35 45 55 65
  • Started at 25: $524,963
  • Started at 35: $243,994
  • Started at 45: $104,185

The Compound Interest Formula

The math behind the growth — every variable explained.

See the formula →
A=P(1+rn)ntA = P\left(1 + \frac{r}{n}\right)^{nt}
A
= final amount (future value)
P
= principal (initial deposit)
r
= annual interest rate (decimal)
n
= times compounded per year
t
= time in years

Everything You Need to Plan and Grow

CompoundFX gives you the tools to model, analyze, and achieve your financial goals.

Free to download, with an optional one-time Pro upgrade. No subscription.

CompoundFX retirement plan screen showing future value, contributions, and a growth chart

Native SwiftUI · iOS 17+ · Fully offline · No third-party SDKs

  • Real-Time Growth Chart

    Watch your projection update live, with milestone markers at $100K, $250K, and $1M.

  • Year-by-Year Breakdown

    See exactly how much you contributed and earned in every single year.

  • Inflation, Tax & Expense Adjustments

    Adjust projections for inflation, taxes, and expense ratios to see real-world outcomes.

  • Goal Mode Pro

    Solves for rate of return, time horizon, starting principal, or monthly contribution.

  • Saved Scenarios & Comparisons Pro

    Save unlimited plans, come back anytime, and compare them side-by-side.

  • Private & Secure

    No accounts, no analytics, no data collection. Everything runs locally on your device.

CompoundFX dashboard on a MacBook with an iPhone alongside

Go beyond the basics with CompoundFX

CompoundFX is free to download, including the full calculation engine, real-time growth charts with milestone markers, year-by-year breakdowns, inflation and tax adjustments, custom contribution schedules, and branded image sharing. An optional one-time Pro purchase unlocks Goal Mode, unlimited saved scenarios, side-by-side scenario comparisons, and two-page PDF reports. No subscription, no accounts, no data collection — everything runs locally on your device.

CompoundFX

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