Compound Interest Calculator
Discover how small monthly deposits can grow into a vast financial safety net over decades. The calculator below strictly maps continuous compound growth without drift to trace EXACT future yields.
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 Compound Interest?
Compound interest represents the interest earned on both your initial principal sum and the accumulated interest from previous periods. Functionally, it allows your wealth to grow simultaneously as your underlying asset yields additional returns on top of older returns, forming an exponential curve rather than a linear slope.
How Often Should Interest Compound?
Most standard index investments mimic compound interest implicitly through capitalization growth mapped yearly. However, formal savings structures or bonds may pay dividends across quarterly or monthly epochs. An interest rate compounding Daily (365 times per annum) generates mathematically optimal yields, although differences over long durations between daily and monthly compounding remain marginal.
Simple vs. Compound Interest
Simple interest is calculated strictly on the original principal. Over 30 years at 10%, a flat simple projection on $10,000 yields $40,000 gross. A compound projection scales far beyond, mapping exponential curves to exceed $174,000 using continuous mathematical models.
* This framework relies directly upon standard closed-form compound interest formulas with full precision, rounding only the final result.
Methodology
This calculator employs standard closed-form compound interest formulas with full precision, rounding only the final result. This prevents cumulative penny-rounding drift from skewing long-term projections over decades. The core mathematical derivation maps the future value of the principal deposit and the future value of ordinary annuities:
* Where P = Principal, r = annual interest rate, n = compound frequency per year, t = years, and PMT = periodic payment amount.
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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.
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