Calculator
Compound Interest Calculator
Enter a starting balance, a monthly deposit, a return rate and a time horizon to see how much of the final balance came from your deposits and how much came from growth.
Balance after 30 years
$252,111
$120,192 in today's dollars at 2.5% inflation
You put in
$73,000
starting balance plus every deposit
Growth
$179,111
71% of the final balance came from growth, not from you
Where the balance comes from
The blue band is money you deposited. The green band above it is growth on money that was already there — the part that gets larger the longer you leave it alone.
- Contributions
- Growth
| Years | Contributions | Growth | Total |
|---|---|---|---|
| 0 | $1,000 | $0 | $1,000 |
| 1 | $3,400 | $151 | $3,551 |
| 2 | $5,800 | $486 | $6,286 |
| 3 | $8,200 | $1,019 | $9,219 |
| 4 | $10,600 | $1,764 | $12,364 |
| 5 | $13,000 | $2,736 | $15,736 |
| 6 | $15,400 | $3,952 | $19,352 |
| 7 | $17,800 | $5,430 | $23,230 |
| 8 | $20,200 | $7,188 | $27,388 |
| 9 | $22,600 | $9,246 | $31,846 |
| 10 | $25,000 | $11,627 | $36,627 |
| 11 | $27,400 | $14,353 | $41,753 |
| 12 | $29,800 | $17,450 | $47,250 |
| 13 | $32,200 | $20,944 | $53,144 |
| 14 | $34,600 | $24,864 | $59,464 |
| 15 | $37,000 | $29,241 | $66,241 |
| 16 | $39,400 | $34,109 | $73,509 |
| 17 | $41,800 | $39,501 | $81,301 |
| 18 | $44,200 | $45,457 | $89,657 |
| 19 | $46,600 | $52,017 | $98,617 |
| 20 | $49,000 | $59,224 | $108,224 |
| 21 | $51,400 | $67,126 | $118,526 |
| 22 | $53,800 | $75,773 | $129,573 |
| 23 | $56,200 | $85,218 | $141,418 |
| 24 | $58,600 | $95,520 | $154,120 |
| 25 | $61,000 | $106,740 | $167,740 |
| 26 | $63,400 | $118,944 | $182,344 |
| 27 | $65,800 | $132,204 | $198,004 |
| 28 | $68,200 | $146,597 | $214,797 |
| 29 | $70,600 | $162,203 | $232,803 |
| 30 | $73,000 | $179,111 | $252,111 |
Reading this result
At 7% a year, money doubles roughly every 10.2 years (the rule of 72 estimates 10.3). That is why the green band starts small and then accelerates: each doubling is larger than the last.
Interest is compounded monthly and deposits are added at the end of each month. The return rate is a fixed assumption — real returns move around every year, and a bad stretch early on matters more than the average suggests.
FAQ
Questions about this calculator
More on this in the investing guides.
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