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Investment Growth

Compound Interest Calculator

See how reinvested returns snowball a starting balance and regular contributions into long-term wealth.

Calculator inputs
$
$
%
yrs

Future balance

$481,947

After 30 years

Total contributions

$100,000

Total interest earned

$381,947

Key insight

Total invested
$100,000
Interest earned
$381,947
Balance from growth
79.25%
  • Starting Balance
  • Contributions
  • Investment Growth
$481,94701530Year 0: Balance $10,000, Total contributions $10,000, Total interest $0Year 0Balance: $10,000Total contributions: $10,000Total interest: $0Year 1: Balance $13,942, Total contributions $13,000, Total interest $942Year 1Balance: $13,942Total contributions: $13,000Total interest: $942Year 2: Balance $18,212, Total contributions $16,000, Total interest $2,212Year 2Balance: $18,212Total contributions: $16,000Total interest: $2,212Year 3: Balance $22,836, Total contributions $19,000, Total interest $3,836Year 3Balance: $22,836Total contributions: $19,000Total interest: $3,836Year 4: Balance $27,844, Total contributions $22,000, Total interest $5,844Year 4Balance: $27,844Total contributions: $22,000Total interest: $5,844Year 5: Balance $33,268, Total contributions $25,000, Total interest $8,268Year 5Balance: $33,268Total contributions: $25,000Total interest: $8,268Year 6: Balance $39,141, Total contributions $28,000, Total interest $11,141Year 6Balance: $39,141Total contributions: $28,000Total interest: $11,141Year 7: Balance $45,503, Total contributions $31,000, Total interest $14,503Year 7Balance: $45,503Total contributions: $31,000Total interest: $14,503Year 8: Balance $52,392, Total contributions $34,000, Total interest $18,392Year 8Balance: $52,392Total contributions: $34,000Total interest: $18,392Year 9: Balance $59,853, Total contributions $37,000, Total interest $22,853Year 9Balance: $59,853Total contributions: $37,000Total interest: $22,853Year 10: Balance $67,933, Total contributions $40,000, Total interest $27,933Year 10Balance: $67,933Total contributions: $40,000Total interest: $27,933Year 11: Balance $76,684, Total contributions $43,000, Total interest $33,684Year 11Balance: $76,684Total contributions: $43,000Total interest: $33,684Year 12: Balance $86,161, Total contributions $46,000, Total interest $40,161Year 12Balance: $86,161Total contributions: $46,000Total interest: $40,161Year 13: Balance $96,425, Total contributions $49,000, Total interest $47,425Year 13Balance: $96,425Total contributions: $49,000Total interest: $47,425Year 14: Balance $107,540, Total contributions $52,000, Total interest $55,540Year 14Balance: $107,540Total contributions: $52,000Total interest: $55,540Year 15: Balance $119,579, Total contributions $55,000, Total interest $64,579Year 15Balance: $119,579Total contributions: $55,000Total interest: $64,579Year 16: Balance $132,616, Total contributions $58,000, Total interest $74,616Year 16Balance: $132,616Total contributions: $58,000Total interest: $74,616Year 17: Balance $146,736, Total contributions $61,000, Total interest $85,736Year 17Balance: $146,736Total contributions: $61,000Total interest: $85,736Year 18: Balance $162,027, Total contributions $64,000, Total interest $98,027Year 18Balance: $162,027Total contributions: $64,000Total interest: $98,027Year 19: Balance $178,588, Total contributions $67,000, Total interest $111,588Year 19Balance: $178,588Total contributions: $67,000Total interest: $111,588Year 20: Balance $196,523, Total contributions $70,000, Total interest $126,523Year 20Balance: $196,523Total contributions: $70,000Total interest: $126,523Year 21: Balance $215,947, Total contributions $73,000, Total interest $142,947Year 21Balance: $215,947Total contributions: $73,000Total interest: $142,947Year 22: Balance $236,983, Total contributions $76,000, Total interest $160,983Year 22Balance: $236,983Total contributions: $76,000Total interest: $160,983Year 23: Balance $259,765, Total contributions $79,000, Total interest $180,765Year 23Balance: $259,765Total contributions: $79,000Total interest: $180,765Year 24: Balance $284,438, Total contributions $82,000, Total interest $202,438Year 24Balance: $284,438Total contributions: $82,000Total interest: $202,438Year 25: Balance $311,158, Total contributions $85,000, Total interest $226,158Year 25Balance: $311,158Total contributions: $85,000Total interest: $226,158Year 26: Balance $340,097, Total contributions $88,000, Total interest $252,097Year 26Balance: $340,097Total contributions: $88,000Total interest: $252,097Year 27: Balance $371,437, Total contributions $91,000, Total interest $280,437Year 27Balance: $371,437Total contributions: $91,000Total interest: $280,437Year 28: Balance $405,379, Total contributions $94,000, Total interest $311,379Year 28Balance: $405,379Total contributions: $94,000Total interest: $311,379Year 29: Balance $442,137, Total contributions $97,000, Total interest $345,137Year 29Balance: $442,137Total contributions: $97,000Total interest: $345,137Year 30: Balance $481,947, Total contributions $100,000, Total interest $381,947Year 30Balance: $481,947Total contributions: $100,000Total interest: $381,947
Year-by-year growth
YearContributionsInterestBalance
1$13,000$942$13,942
2$16,000$2,212$18,212
3$19,000$3,836$22,836
4$22,000$5,844$27,844
5$25,000$8,268$33,268
6$28,000$11,141$39,141
7$31,000$14,503$45,503
8$34,000$18,392$52,392
9$37,000$22,853$59,853
10$40,000$27,933$67,933
11$43,000$33,684$76,684
12$46,000$40,161$86,161
13$49,000$47,425$96,425
14$52,000$55,540$107,540
15$55,000$64,579$119,579
16$58,000$74,616$132,616
17$61,000$85,736$146,736
18$64,000$98,027$162,027
19$67,000$111,588$178,588
20$70,000$126,523$196,523
21$73,000$142,947$215,947
22$76,000$160,983$236,983
23$79,000$180,765$259,765
24$82,000$202,438$284,438
25$85,000$226,158$311,158
26$88,000$252,097$340,097
27$91,000$280,437$371,437
28$94,000$311,379$405,379
29$97,000$345,137$442,137
30$100,000$381,947$481,947

How it's calculated

Formula

FV = P(1 + r/12)^(12t) + PMT · [((1 + r/12)^(12t) − 1) / (r/12)]

How it works

The formula has two parts. The first term grows your starting balance by the monthly rate (r/12), compounded for every month (12t). The second term is the future value of your monthly contributions: each deposit compounds for the months remaining after it's made, and the bracket totals them up. Add the two and you get the ending balance.

Variables

FV
Future value (ending balance)
P
Starting balance (principal)
PMT
Monthly contribution
r
Annual interest rate (decimal form). Example: 8% = 0.08
t
Number of years

Worked example

Starting Balance $1,000 Annual Interest Rate 6% Years 10 Monthly Interest Rate 0.06 ÷ 12 = 0.005 Total Months 12 × 10 = 120 Calculation FV = 1,000 × (1 + 0.005)^120 ≈ $1,819 Result After 10 years, $1,000 grows to approximately $1,819 through monthly compounding.

Frequently asked questions

What compounding frequency is assumed?

Monthly. Interest is compounded once per month and each contribution is added at the end of the month, which mirrors how most brokerage and retirement accounts behave.

Is the return guaranteed?

No. The annual return is an assumption you choose, not a promise. Real market returns vary year to year and can be negative — try a range of rates to see optimistic and conservative outcomes.

Does this include inflation?

No. Results are in nominal dollars. Because inflation erodes purchasing power over time, $1 in 30 years buys less than $1 today — use the Inflation calculator to see the real value.

Does it account for taxes?

No. Growth is shown before taxes. In a taxable account, dividends and gains may be taxed along the way; tax-advantaged accounts like a 401(k) or IRA defer or avoid some of that. Your actual after-tax result may be lower.

Can I include regular contributions?

Yes. Set a monthly contribution and it's added every month and compounded for the remaining time. Contributions are usually the biggest driver of the final balance early on, with growth taking over later.

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