Compound Interest Calculator
See how your savings or investments grow with compound interest, from a starting amount, a fixed monthly contribution and a savings goal.
Final amount
$31,998.32
Monthly
Total contributed
$22,000.00
Total interest
$9,998.32
Savings goal reached after
7 years and 4 months
Final amount: contributions and interest
- Contributed $22,000.00 68.8%
- Interest $9,998.32 31.3%
Total $31,998.32
How your money grows
- Contributed
- Interest earned
Show the table
| Year | Contributed | Interest earned |
|---|---|---|
| 0 | $10,000.00 | $0.00 |
| 1 | $11,200.00 | $539.50 |
| 2 | $12,400.00 | $1,168.01 |
| 3 | $13,600.00 | $1,890.06 |
| 4 | $14,800.00 | $2,710.44 |
| 5 | $16,000.00 | $3,634.20 |
| 6 | $17,200.00 | $4,666.60 |
| 7 | $18,400.00 | $5,813.23 |
| 8 | $19,600.00 | $7,079.91 |
| 9 | $20,800.00 | $8,472.79 |
| 10 | $22,000.00 | $9,998.32 |
Please note: This is an example calculation, not financial advice. Personal circumstances, changes in rules and rates, and additional costs are not included. If in doubt, talk to a financial adviser.
Taxes, fees and inflation are not included, and the interest rate stays the same for the whole period.
How this number is calculated
The blocks use your input. Change a value above and they update with it.
Step 1 · Number of compounding periods
Step 2 · Interest per period
Step 3 · Growth factor per period
Step 4 · Contribution per period
Step 5 · Growth factor
Step 6 · Starting amount with interest
Step 7 · Contributions with interest
Step 8 · Final amount
Step 9 · Total contributed
Step 10 · Total interest
How the calculation works
With compound interest you earn interest not only on the money you put in, but also on the interest you have already earned. That makes your money grow a little faster every year. Enter your starting amount, monthly contribution, interest rate, number of years and a savings goal. You see what you end up with, how much of it is contributions and how much is interest for every year, and after how many months you reach your goal.
Monthly contributions are added at the end of each month. With monthly compounding, one twelfth of the annual rate is added every month. With yearly compounding, the calculator treats a full year of contributions (12 times your monthly amount) as one deposit at the end of that year, and interest is added once a year. The final amount is rounded to the cent; the interest is the final amount minus everything you put in. The chart shows your balance for every year, split into what you put in yourself and what the interest added; at any rate above 0% the interest part grows every year. For the savings goal, the calculator finds the first month in which your balance, rounded to the cent, is at least the goal. The result is an estimate: taxes, fees and inflation are not included, and the interest rate stays the same for the whole period.
Formula
Growth factor = (1 + r)^n, where r is the interest per period (annual rate ÷ 100 ÷ 12 for monthly, ÷ 1 for yearly) and n is the number of periods. Final amount = starting amount × growth factor + contribution per period × (growth factor − 1) ÷ r. At 0% interest: final amount = starting amount + all contributions. Savings goal: the first month m in which starting amount × (1 + r)^k + contribution per period × ((1 + r)^k − 1) ÷ r is at least the goal, where k is the number of periods up to and including month m.
Assumptions
- The interest rate stays the same for the whole period.
- Taxes, fees and inflation are not included.
- Contributions are added at the end of each month; with yearly compounding, a year of contributions counts as one deposit at the end of that year.
- Nothing is withdrawn along the way.
- The savings goal counts in whole months: it is the first month in which your balance at the end of that month is at least the goal.
- With yearly compounding the balance only grows at the end of each year, so the savings goal is then always reached at a year end.
- A savings goal of 0 counts as no goal.
Example calculations
The button fills in the calculator above, so you can carry on from there.
-
Savings with monthly deposits
Final amount
$8,677.76
Starting amount $5,000.00 · Monthly contribution $50.00 · Annual interest rate (%) 2 · Years 5 · Monthly · Savings goal $0.00
-
Saving for a child
Final amount
$7,148.51
Starting amount $0.00 · Monthly contribution $25.00 · Annual interest rate (%) 3 · Years 18 · Monthly · Savings goal $0.00
-
One-off lump sum
Final amount
$21,911.23
Starting amount $10,000.00 · Monthly contribution $0.00 · Annual interest rate (%) 4 · Years 20 · Yearly · Savings goal $20,000.00
With 20,000 as the savings goal you see when the amount has doubled: after 216 months, exactly 18 years.
-
Savings goal in sight
Final amount
$47,178.18
Starting amount $2,500.00 · Monthly contribution $150.00 · Annual interest rate (%) 3 · Years 18 · Monthly · Savings goal $30,000.00
Start with 2,500 and add 150 a month at 3%: the savings goal of 30,000 is reached after 147 months.
Frequently asked questions
What is compound interest?
The interest you earn is added to your balance and then earns interest itself. Put 1,000 in at 5% and you have 1,050 after one year; the next year you earn 5% on 1,050. After 10 years that adds up to 1,628.89, compared with 1,500 if you only earned interest on the original 1,000. The chart shows the effect: the interest part gets bigger every year.
What is the difference between monthly and yearly compounding?
With monthly compounding, one twelfth of the annual rate is added every month, and that interest starts earning interest the next month. The result is slightly higher: 1,000 at 5% grows to 1,647.01 in 10 years with monthly compounding, and to 1,628.89 with yearly compounding. With yearly compounding the balance only grows at the end of each year, so the savings goal is then also reached at a year end.
How does the savings goal work?
Enter the amount you want to reach. The calculator finds the first month in which your balance reaches it and shows the number of months: 159 months is 13 years and 3 months. If the goal is not reached within the term, or you enter 0, it says so. This also shows when your money doubles: 10,000 at 4% compounded yearly becomes 20,000 after 216 months, just as the rule of 72 predicts (72 ÷ 4 = 18 years).
Does the result include inflation?
No, the result is in future money, not in today's buying power. A rough way to allow for inflation is to enter the interest rate minus the expected inflation; the result is then roughly in today's money.
What is the effective annual rate (APY or AER)?
It is the yearly rate including the effect of compounding. 5% compounded monthly works out at (1 + 0.05 ÷ 12)^12 − 1 = 5.12% a year. If your bank quotes an APY or AER, choose yearly compounding so the compounding is not counted twice.
Can I use this calculator for investments?
Yes, as a rough illustration: enter an average yearly return as the rate. Real returns go up and down from year to year and can be negative, so the actual result can differ a lot from the smooth growth shown here.
Sources and checks
Sources
How we check it
This calculator has 30 fixed checks: 24 calculations with a result that is fixed in advance, and 6 cases of invalid input that must be rejected. They all run automatically every time we publish; if one fails, the calculator does not go live.
See the calculations
- Starting amount $10,000.00 · Monthly contribution $100.00 · Annual interest rate (%) 5 · Years 10 · Monthly · Savings goal $25,000.00 → Final amount $31,998.32
- Starting amount $1,000.00 · Monthly contribution $0.00 · Annual interest rate (%) 5 · Years 10 · Yearly · Savings goal $0.00 → Final amount $1,628.89
- Starting amount $1,000.00 · Monthly contribution $0.00 · Annual interest rate (%) 5 · Years 10 · Monthly · Savings goal $0.00 → Final amount $1,647.01
- Starting amount $0.00 · Monthly contribution $100.00 · Annual interest rate (%) 5 · Years 10 · Monthly · Savings goal $0.00 → Final amount $15,528.23
- Starting amount $0.00 · Monthly contribution $100.00 · Annual interest rate (%) 5 · Years 10 · Yearly · Savings goal $0.00 → Final amount $15,093.47
- Starting amount $1,000.00 · Monthly contribution $100.00 · Annual interest rate (%) 0 · Years 10 · Monthly · Savings goal $0.00 → Final amount $13,000.00
- Starting amount $1,000.00 · Monthly contribution $100.00 · Annual interest rate (%) 0 · Years 10 · Yearly · Savings goal $0.00 → Final amount $13,000.00
- Starting amount $1.00 · Monthly contribution $0.00 · Annual interest rate (%) 0.5 · Years 1 · Yearly · Savings goal $0.00 → Final amount $1.01
- Starting amount $1,000.00 · Monthly contribution $100.00 · Annual interest rate (%) 6 · Years 1 · Monthly · Savings goal $0.00 → Final amount $2,295.23
- Starting amount $1,000.00 · Monthly contribution $0.00 · Annual interest rate (%) 7 · Years 60 · Yearly · Savings goal $0.00 → Final amount $57,946.43
Changes
- : Sources added and content reviewed.
- : First version.
Last reviewed: · How we build and check our calculators
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