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Compound Interest Calculator: Savings Growth With Monthly Deposits
Start with what you have, add what you plan to save each month, and see what compounding turns it into. Compare compounding frequencies, try a range of rates, and see the result in today's money if you enter an inflation rate.
- Daily, monthly, quarterly, yearly or continuous
- Deposits on their own schedule, start or end
- Rate range and today's-money value
Compound interest calculator
Your savings
Leave at 0 if you only add regular amounts.
The nominal rate, before compounding.
0–11, added to the years.
How often interest is added to the balance.
Regular contributions
Leave at 0 for a single deposit.
Added at the
What if
Returns are rarely fixed. See a range, and what the balance would buy in today's money.
Shows the balance at this many points below and above your rate.
Your assumption. Leave empty to skip.
- Balance
- Money put in
Growth by yearShow
| Year | Contributions | Interest | Closing balance | Total interest |
|---|---|---|---|---|
| 1 | $2,400.00 | $801.42 | $13,201.42 | $801.42 |
| 2 | $2,400.00 | $1,032.85 | $16,634.27 | $1,834.27 |
| 3 | $2,400.00 | $1,281.01 | $20,315.28 | $3,115.28 |
| 4 | $2,400.00 | $1,547.11 | $24,262.39 | $4,662.39 |
| 5 | $2,400.00 | $1,832.44 | $28,494.83 | $6,494.83 |
| 6 | $2,400.00 | $2,138.41 | $33,033.24 | $8,633.24 |
| 7 | $2,400.00 | $2,466.50 | $37,899.74 | $11,099.74 |
| 8 | $2,400.00 | $2,818.29 | $43,118.03 | $13,918.03 |
| 9 | $2,400.00 | $3,195.52 | $48,713.55 | $17,113.55 |
| 10 | $2,400.00 | $3,600.03 | $54,713.58 | $20,713.58 |
| 11 | $2,400.00 | $4,033.76 | $61,147.34 | $24,747.34 |
| 12 | $2,400.00 | $4,498.86 | $68,046.20 | $29,246.20 |
| 13 | $2,400.00 | $4,997.59 | $75,443.79 | $34,243.79 |
| 14 | $2,400.00 | $5,532.35 | $83,376.14 | $39,776.14 |
| 15 | $2,400.00 | $6,105.79 | $91,881.93 | $45,881.93 |
| 16 | $2,400.00 | $6,720.67 | $101,002.60 | $52,602.60 |
| 17 | $2,400.00 | $7,380.00 | $110,782.60 | $59,982.60 |
| 18 | $2,400.00 | $8,087.00 | $121,269.60 | $68,069.60 |
| 19 | $2,400.00 | $8,845.10 | $132,514.70 | $76,914.70 |
| 20 | $2,400.00 | $9,658.02 | $144,572.72 | $86,572.72 |
Compound Interest Formula
A = P × (1 + r/n)^(n × t)
| Symbol | Meaning |
|---|---|
| A | Balance at the end |
| P | Starting amount (principal) |
| r | Yearly interest rate as a decimal: 5% = 0.05 |
| n | Times interest is added each year: 1, 2, 4, 12 or 365 |
| t | Years |
The interest earned is A − P. When interest is added continuously, the formula becomes A = P × e^(r × t).
With a Deposit Every Period
A = P × (1 + i)^N + C × ((1 + i)^N − 1) ÷ i
Here C is the deposit, i = r ÷ n is the rate per period and N = n × t is the number of periods. That assumes each deposit is made at the end of a period. If you pay in at the start, multiply the deposit part by (1 + i).
If you pay in monthly but the account compounds quarterly or daily, the periods don't line up. The calculator then turns the rate into its effective annual rate, (1 + r/n)^n − 1, and from that into a rate for each month.
Daily, Monthly or Yearly Compounding: How Much Does It Change?
10,000 left for 10 years at an example rate of 5%, with no further deposits:
| Interest added | Balance after 10 years | Interest earned | APY |
|---|---|---|---|
| Once a year | 16,288.95 | 6,288.95 | 5.000% |
| Twice a year | 16,386.16 | 6,386.16 | 5.063% |
| Quarterly | 16,436.19 | 6,436.19 | 5.095% |
| Monthly | 16,470.09 | 6,470.09 | 5.116% |
| Daily | 16,486.65 | 6,486.65 | 5.127% |
| Continuously | 16,487.21 | 6,487.21 | 5.127% |
Going from yearly to monthly adds 181.14. Going from monthly to daily adds 16.56. Compounding frequency matters most at high rates and over long periods; for a savings account, a higher rate beats a more frequent schedule.
What 200 a Month Grows Into
This is the example loaded in the calculator: 10,000 to start, 200 paid in at the end of each month, an example 7% compounded monthly, for 20 years.
| Amount | |
|---|---|
| Starting amount | 10,000.00 |
| 240 deposits of 200 | 48,000.00 |
| Interest | 86,572.72 |
| Balance after 20 years | 144,572.72 |
The first 10 years earn 20,713.58 of interest. The second 10 years earn 65,859.14, more than three times as much, because interest is now being paid on interest. Money left to compound for longest does most of the work, which is why starting earlier usually beats saving more later.
The Same Plan at Other Rates
Returns are rarely fixed, so the calculator also runs your plan two points either side of your rate:
| Rate | Balance after 20 years |
|---|---|
| 5% | 109,333.14 |
| 7% | 144,572.72 |
| 9% | 193,668.89 |
Four points of difference in the rate move the result by 84,335.75, which is more than everything paid in.
In Today's Money
A balance 20 years from now will buy less than the same amount today. At an assumed 3% inflation, 144,572.72 in 20 years buys what 80,046.41 buys now. Enter an inflation rate in the calculator to see this for your plan.
Rule of 72: How Long Until Your Money Doubles?
Divide 72 by the yearly rate to estimate how many years a lump sum takes to double. The exact answer, with yearly compounding, is ln(2) ÷ ln(1 + r):
| Rate | Rule of 72 | Exact |
|---|---|---|
| 2% | 36.0 years | 35.0 years |
| 4% | 18.0 years | 17.7 years |
| 6% | 12.0 years | 11.9 years |
| 8% | 9.0 years | 9.0 years |
| 10% | 7.2 years | 7.3 years |
| 12% | 6.0 years | 6.1 years |
The shortcut is closest around 8%. The calculator shows the exact figure for your rate and compounding.
APY, AER and the Effective Annual Rate
Banks advertise two numbers. The nominal rate is the yearly rate before compounding. The effective rate includes compounding: APY in the United States, AER in the United Kingdom, or simply the effective annual rate. A 5% rate compounded monthly has an effective rate of 5.116%.
To compare accounts, use the effective rate. To model an account in this calculator, enter the nominal rate with its compounding frequency, or enter the APY with yearly compounding; both give the same balance.
When Compounding Works Against You
The same maths applies to debt. Unpaid credit card interest is added to the balance, and next month's interest is charged on it. That is why a card balance left alone grows quickly. To see the cost of a card balance and how long it takes to clear, use the credit card interest calculator. Compound interest also differs from flat interest on the original amount, which the simple interest calculator covers.
The rates on this page are examples. Savings rates change, investment returns are not guaranteed, and the balance shown is before tax and fees.
Updated . How we check our tools and content.
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Compound Interest Calculator FAQ
Compounding, APY, doubling time and deposits, in plain numbers.
How do you calculate compound interest?
Use A = P × (1 + r/n)^(n × t) and subtract P. P is the starting amount, r the yearly rate as a decimal, n how many times a year interest is added, and t the number of years. For 10,000 at 5% compounded monthly for 10 years: 10,000 × (1 + 0.05/12)^120 = 16,470.09, so the interest is 6,470.09.
How much will 10,000 grow to in 10 years?
It depends on the rate and how often interest is added. At an example 5% it becomes 16,288.95 with yearly compounding and 16,470.09 with monthly compounding. Enter your own rate above; the rate matters far more than the frequency.
Is daily compounding much better than monthly?
Barely, at savings-account rates. On 10,000 at 5% for 10 years, daily compounding beats monthly by 16.56. Choose an account on its APY, which already includes the compounding frequency, rather than on how often it compounds.
How long does it take to double my money?
Divide 72 by the yearly rate for a quick estimate. At 6% that is 12 years; the exact figure with yearly compounding is 11.9. The rule works best between about 6% and 10% and drifts at very low or high rates, so the calculator shows the exact doubling time instead.
What is the difference between the interest rate and APY?
The interest rate is the yearly rate before compounding. APY (called AER in the UK) is what you actually earn in a year once compounding is included. 5% compounded monthly is an APY of 5.116%. To compare an APY with this calculator, enter the APY as the rate and choose yearly compounding.
Do deposits at the start of the month earn more?
Yes, one extra month of interest on each deposit. In the example, paying the 200 at the start of each month instead of the end gives 145,180.47 instead of 144,572.72 after 20 years.
What is my balance worth after inflation?
Divide it by (1 + inflation)^years. 144,572.72 in 20 years, at an assumed 3% a year inflation, buys what 80,046.41 buys today. Enter your own inflation assumption in the What if section; the calculator does not use official inflation data.
How are deposits handled when they don't match the compounding schedule?
The calculator converts the rate to its effective annual rate and then to an equivalent monthly rate, so a monthly deposit into a quarterly-compounding account earns interest for the part of the quarter it is invested. Some banks pay nothing between compounding dates, which gives a slightly lower figure.
Is the result before tax?
Yes. Interest is usually taxable unless it is earned in a tax-advantaged account, and the rules depend on your country, so no tax is deducted.