$
$
%
20 yr
Starting amount$10,000
Total contributions$130,000
Interest earned$170,851
Future value$300,851
The split
Contributions 43%Interest 57%

Growth over time

Today20 years

Year by year

YrContributedInterestBalance
1$16,000$919$16,919
2$22,000$2,339$24,339
3$28,000$4,294$32,294
4$34,000$6,825$40,825
5$40,000$9,973$49,973
6$46,000$13,782$59,782
7$52,000$18,299$70,299
8$58,000$23,578$81,578
9$64,000$29,671$93,671
10$70,000$36,639$106,639
11$76,000$44,544$120,544
12$82,000$53,455$135,455
13$88,000$63,443$151,443
14$94,000$74,587$168,587
15$100,000$86,971$186,971
16$106,000$100,683$206,683
17$112,000$115,820$227,820
18$118,000$132,486$250,486
19$124,000$150,790$274,790
20$130,000$170,851$300,851

The formula

FV=P(1+i)n+PMT⋅(1+i)n−1iFV = P(1+i)^n + PMT \cdot \dfrac{(1+i)^n - 1}{i}
P — starting principal
PMT — monthly contribution
i — monthly rate (annual ÷ 12)
n — months (years × 12)

How it works

Compounding means you earn returns on your returns. Contributions add up linearly, but the growth curve bends upward over time as interest starts earning interest of its own — which is why starting early matters so much.

FAQ

Is this adjusted for inflation?

No — these are nominal figures. Real purchasing power will be lower depending on future inflation.

How often does it compound?

Monthly, with contributions added at the end of each month.

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Why compound interest grows so fast

Compounding means you earn returns not only on your original deposit but also on the returns already added. Over a few years the effect is modest, but across decades the growth curve bends sharply upward as interest starts earning interest of its own. This is why starting early usually matters more than investing larger amounts later on. The balance after nn months is FV=P(1+i)n+PMT (1+i)n−1iFV = P(1+i)^n + PMT\,\frac{(1+i)^n-1}{i}, where ii is the monthly rate.

Contributions versus growth

Two forces build the final balance: the money you put in — your starting amount plus every monthly contribution — and the interest earned on it. Early on, contributions dominate. Later, growth takes over and can end up larger than everything you contributed combined. The split shown here makes that crossover visible.

A note on the assumptions

These are nominal figures compounded monthly, with contributions added at the end of each month. Real returns vary from year to year and inflation erodes future purchasing power, so treat the result as a projection rather than a guarantee.