Compound Interest & Investment Growth Calculator
Model long-term wealth accumulation and investment compounding curves. Analyze how periodic deposits, compounding frequency, and annual rates of return scale your portfolio value over decades.
Estimated Final Balance
Projection Curve
| Year | Starting Balance | Contributions | Interest Earned | Ending Balance |
|---|---|---|---|---|
| Year 1 | $10,000.00 | $3,000.00 | +$821.05 | $13,821.05 |
| Year 2 | $13,821.05 | $3,000.00 | +$1,097.27 | $17,918.32 |
| Year 3 | $17,918.32 | $3,000.00 | +$1,393.46 | $22,311.78 |
| Year 4 | $22,311.78 | $3,000.00 | +$1,711.07 | $27,022.85 |
| Year 5 | $27,022.85 | $3,000.00 | +$2,051.63 | $32,074.48 |
| Year 6 | $32,074.48 | $3,000.00 | +$2,416.81 | $37,491.29 |
| Year 7 | $37,491.29 | $3,000.00 | +$2,808.39 | $43,299.69 |
| Year 8 | $43,299.69 | $3,000.00 | +$3,228.28 | $49,527.97 |
| Year 9 | $49,527.97 | $3,000.00 | +$3,678.53 | $56,206.50 |
| Year 10 | $56,206.50 | $3,000.00 | +$4,161.32 | $63,367.82 |
| Year 11 | $63,367.82 | $3,000.00 | +$4,679.01 | $71,046.83 |
| Year 12 | $71,046.83 | $3,000.00 | +$5,234.13 | $79,280.95 |
| Year 13 | $79,280.95 | $3,000.00 | +$5,829.37 | $88,110.33 |
| Year 14 | $88,110.33 | $3,000.00 | +$6,467.65 | $97,577.98 |
| Year 15 | $97,577.98 | $3,000.00 | +$7,152.07 | $107,730.04 |
| Year 16 | $107,730.04 | $3,000.00 | +$7,885.96 | $118,616.00 |
| Year 17 | $118,616.00 | $3,000.00 | +$8,672.91 | $130,288.91 |
| Year 18 | $130,288.91 | $3,000.00 | +$9,516.74 | $142,805.65 |
| Year 19 | $142,805.65 | $3,000.00 | +$10,421.58 | $156,227.23 |
| Year 20 | $156,227.23 | $3,000.00 | +$11,391.83 | $170,619.05 |
| Year 21 | $170,619.05 | $3,000.00 | +$12,432.21 | $186,051.26 |
| Year 22 | $186,051.26 | $3,000.00 | +$13,547.81 | $202,599.07 |
| Year 23 | $202,599.07 | $3,000.00 | +$14,744.05 | $220,343.12 |
| Year 24 | $220,343.12 | $3,000.00 | +$16,026.77 | $239,369.89 |
| Year 25 | $239,369.89 | $3,000.00 | +$17,402.22 | $259,772.11 |
| Year 26 | $259,772.11 | $3,000.00 | +$18,877.09 | $281,649.20 |
| Year 27 | $281,649.20 | $3,000.00 | +$20,458.59 | $305,107.79 |
| Year 28 | $305,107.79 | $3,000.00 | +$22,154.41 | $330,262.20 |
| Year 29 | $330,262.20 | $3,000.00 | +$23,972.83 | $357,235.03 |
| Year 30 | $357,235.03 | $3,000.00 | +$25,922.70 | $386,157.72 |
What is the Rule of 72 and how is it used?
The Rule of 72 is a simple mathematical shortcut used to estimate the number of years required to double your invested capital at a fixed annual rate of interest. By dividing 72 by your expected annual rate of return (e.g., 72 / 8 = 9), you get the approximate doubling time in years (9 years). It provides a quick way to conceptualize the compounding velocity of different asset classes.
How does compounding frequency affect investment returns?
Compounding frequency dictates how often interest is calculated and added back to the principal. Standard options include annual, semi-annual, quarterly, monthly, and daily compounding. More frequent intervals allow interest to accrue on accumulated interest faster, raising the Effective Annual Yield (EAY) above the nominal interest rate. While daily compounding generates mathematically optimal yields, the practical divergence from monthly or quarterly compounding is relatively minor over short time horizons but increases significantly over multi-decade scales.
Is it better to invest a lump-sum or make regular contributions?
A lump-sum investment puts all your capital to work immediately, maximizing compounding potential from day one if the asset experiences positive returns. In contrast, regular contributions (such as monthly deposits) leverage dollar-cost averaging. This disciplined approach builds savings systematically, mitigates the risk of buying at market peaks, and compounds each contribution from its respective deposit date onwards.
Methodology
To model long-term financial growth without margin of error, this calculator computes compound interest using a continuous closed-form algebraic model. By executing all calculations in full precision and rounding only the final value, the engine completely eliminates daily rounding drift to guarantee mathematically perfect projections over multi-decade horizons. The underlying formula aggregates the compounding growth of your starting principal alongside a structured recurring contribution annuity:
When "Continuous" compounding is selected, the calculator instead uses the n → ∞ limit formula FV = P·ert + (C/r)(ert − 1) rather than periodic compounding, where C is the annual contribution.
* Where P = Principal (starting deposit), r = annual interest rate, n = compounding frequency per year, t = duration in years, and PMT = periodic payment amount (contribution).
Related Tools
Bret Mishler
Bret Mishler is the founder and lead developer of MoneyMage. As a Senior Software Engineer and Tech Lead specializing in enterprise-scale cloud billing systems, Bret brings production-grade financial engineering rigor to personal finance. He built MoneyMage to deliver mathematically transparent, lightning-fast financial tools — applying the same strict precision required to process billions of dollars in cloud infrastructure to your personal wealth.
LinkedIn Profile