Compound Interest
How much will my money grow if I keep saving?
When you save or invest, you earn interest — and then you earn interest on that interest too. This calculator shows how much your money could grow over time, and how much of it comes from you versus from growth.
How to use this calculatorShowHide
- Step 1: Enter what you have now and how much you plan to add regularly (for example, $100 a month).
- Step 2: Enter a yearly growth rate and how many years you'll keep saving. Not sure what rate to use? Check the hint under the field.
- Step 3: Read the big number at the top — that's what you could have. The chart shows how much you put in versus how much grew on its own.
What you'll need
- How much you have saved or invested today (can be $0)
- How much you can add each month or paycheck
- Your account's interest rate — shown in your bank or investment app as “APY” or “rate”
Don't know a number? Leave the example value in, or tap the ⓘ next to it. New to this? Read the Beginner's Guide →
Future balance
$691,150.47
If you invest $10,000 and add $500 a month at 7% for 30 years, you'll have about $691,150. You put in $190,000 — the other $501,150 is interest working for you.
- Total contributed
- $190,000.00
- Total interest earned
- $501,150.47
- Interest share of balance
- 72.5%
| Year | Contributions | Interest | Total contributed | Total interest | Balance |
|---|---|---|---|---|---|
| 1 | $6,000.00 | $919.19 | $16,000.00 | $919.19 | $16,919.19 |
| 2 | $6,000.00 | $1,419.38 | $22,000.00 | $2,338.58 | $24,338.58 |
| 3 | $6,000.00 | $1,955.73 | $28,000.00 | $4,294.31 | $32,294.31 |
| 4 | $6,000.00 | $2,530.85 | $34,000.00 | $6,825.16 | $40,825.16 |
| 5 | $6,000.00 | $3,147.55 | $40,000.00 | $9,972.70 | $49,972.70 |
| 6 | $6,000.00 | $3,808.82 | $46,000.00 | $13,781.53 | $59,781.53 |
| 7 | $6,000.00 | $4,517.90 | $52,000.00 | $18,299.43 | $70,299.43 |
| 8 | $6,000.00 | $5,278.24 | $58,000.00 | $23,577.68 | $81,577.68 |
| 9 | $6,000.00 | $6,093.55 | $64,000.00 | $29,671.22 | $93,671.22 |
| 10 | $6,000.00 | $6,967.79 | $70,000.00 | $36,639.02 | $106,639.02 |
| 11 | $6,000.00 | $7,905.24 | $76,000.00 | $44,544.25 | $120,544.25 |
| 12 | $6,000.00 | $8,910.45 | $82,000.00 | $53,454.70 | $135,454.70 |
| 13 | $6,000.00 | $9,988.32 | $88,000.00 | $63,443.02 | $151,443.02 |
| 14 | $6,000.00 | $11,144.12 | $94,000.00 | $74,587.14 | $168,587.14 |
| 15 | $6,000.00 | $12,383.47 | $100,000.00 | $86,970.62 | $186,970.62 |
| 16 | $6,000.00 | $13,712.41 | $106,000.00 | $100,683.03 | $206,683.03 |
| 17 | $6,000.00 | $15,137.43 | $112,000.00 | $115,820.45 | $227,820.45 |
| 18 | $6,000.00 | $16,665.45 | $118,000.00 | $132,485.91 | $250,485.91 |
| 19 | $6,000.00 | $18,303.94 | $124,000.00 | $150,789.85 | $274,789.85 |
| 20 | $6,000.00 | $20,060.87 | $130,000.00 | $170,850.72 | $300,850.72 |
| 21 | $6,000.00 | $21,944.82 | $136,000.00 | $192,795.53 | $328,795.53 |
| 22 | $6,000.00 | $23,964.95 | $142,000.00 | $216,760.48 | $358,760.48 |
| 23 | $6,000.00 | $26,131.12 | $148,000.00 | $242,891.60 | $390,891.60 |
| 24 | $6,000.00 | $28,453.88 | $154,000.00 | $271,345.48 | $425,345.48 |
| 25 | $6,000.00 | $30,944.55 | $160,000.00 | $302,290.03 | $462,290.03 |
| 26 | $6,000.00 | $33,615.28 | $166,000.00 | $335,905.30 | $501,905.30 |
| 27 | $6,000.00 | $36,479.07 | $172,000.00 | $372,384.37 | $544,384.37 |
| 28 | $6,000.00 | $39,549.88 | $178,000.00 | $411,934.26 | $589,934.26 |
| 29 | $6,000.00 | $42,842.69 | $184,000.00 | $454,776.94 | $638,776.94 |
| 30 | $6,000.00 | $46,373.53 | $190,000.00 | $501,150.47 | $691,150.47 |
What this means
In plain English
When your money earns interest, that interest gets added to your balance. Next time, you earn interest on the bigger balance — so you earn interest on your interest. That's compound interest, and it's why money left alone for a long time can grow surprisingly large.
When to use it
- Seeing how much regular saving (like $100 a month) could add up to
- Comparing "start now" against "start in five years"
- Understanding why time matters more than almost anything else
Example
Put $10,000 in an account earning 5% a year (added monthly) and leave it for 10 years. You'd end up with $16,470.09 — that's $6,470.09 you never had to add yourself.
Or start with nothing and save $500 a month at 7% for 30 years. You'd put in $180,000, but end with about $609,985. More than two-thirds of that is growth.
Watch out for
Waiting to start. Saving $500 a month from age 25 to 65 at 7% grows to about $1.3 million. Start at 35 instead and you end up with about $610,000 — less than half, even though you only skipped 10 years.
Also remember: investment returns aren't guaranteed. Some years go up, some go down. The rate you enter is a long-term average.
The math (optional)
For one deposit: A = P × (1 + r/n)^(n × t)
- P — what you start with
- r — the yearly rate as a decimal (7% → 0.07)
- n — how many times a year interest is added
- t — years
With regular deposits, the calculator works through every deposit one at a time using the rate per deposit period: (1 + r/n)^(n/p) − 1, where p is how often you deposit.