Ten years of steady saving
Start with $10,000.00, add $200.00 at the end of each month, at 7% a year for 10 years (120 deposits).
Future value $54,713.58. You put in $34,000.00. Interest is $20,713.58.
Compound interest calculator with monthly deposits
Start with a lump sum, add the same amount every month, and see the balance after compound growth. The split shows money you put in versus interest.
Symbol only. Amounts are not converted.
%
Partial years round to the nearest month.
Future value
$54,713.58
120 monthly deposits.
- You put in
- $34,000.00
- Interest
- $20,713.58
0510
Next: Savings goal calculatorHow much a month that target needs.
Deposits at the end of each month. Nominal annual rate, compounded monthly.
The numbers, period by period
| Period | You put in | Interest | Balance |
|---|---|---|---|
| Year 1 | $12,400.00 | $801.42 | $13,201.42 |
| Year 2 | $14,800.00 | $1,834.27 | $16,634.27 |
| Year 3 | $17,200.00 | $3,115.28 | $20,315.28 |
| Year 4 | $19,600.00 | $4,662.39 | $24,262.39 |
| Year 5 | $22,000.00 | $6,494.83 | $28,494.83 |
| Year 6 | $24,400.00 | $8,633.24 | $33,033.24 |
| Year 7 | $26,800.00 | $11,099.74 | $37,899.74 |
| Year 8 | $29,200.00 | $13,918.03 | $43,118.03 |
| Year 9 | $31,600.00 | $17,113.55 | $48,713.55 |
| Year 10 | $34,000.00 | $20,713.58 | $54,713.58 |
How this is calculated
- Step 1
Opening balance
What is already there at the start of the month.
- Step 2
Interest
The annual rate divided by 12, on that opening balance.
- Step 3
Deposit
Arrives at the end of the month, so it does not earn yet.
Future value of a lump sum plus an ordinary annuity
FV = P(1 + r/12)^(12t) + PMT × [((1 + r/12)^(12t) − 1) ÷ (r/12)]
| P | Starting balance. |
|---|---|
| PMT | Amount added at the end of each month. |
| r | Annual rate as a decimal. 7% is 0.07. |
| t | Time in years. Partial years round to the nearest month. |
The first term is the starting balance, compounded once a month. The second term adds every later deposit, each of which compounds only for the months after it arrives.
If the rate is 0, there is no exponent. The balance is the starting amount plus every deposit.
The SIP calculator places each deposit at the beginning of the month, so the same inputs finish a little higher. The savings goal calculator runs this end-of-month formula backward.
Worked examples
Loading an example fills the tool and scrolls you back to the result. Money examples stay in US dollars on the page. The symbol you picked changes; the numbers do not convert.
A year with no interest
Start with $1,000.00, add $100.00 at the end of each month, at 0% a year for 1 years (12 deposits).
Future value $2,200.00. You put in $2,200.00. Interest is $0.00.
Deposits only, for twenty years
Start with $0.00, add $500.00 at the end of each month, at 6% a year for 20 years (240 deposits).
Future value $231,020.45. You put in $120,000.00. Interest is $111,020.45.
A lump sum left alone
Start with $25,000.00, add $0.00 at the end of each month, at 5% a year for 15 years (180 deposits).
Future value $52,842.60. You put in $25,000.00. Interest is $27,842.60.
Embed this calculator
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<iframe src="/embed/compound-interest" title="Compound interest calculator" width="100%" height="720" style="border:0;max-width:42rem" loading="lazy"></iframe>Questions
Are deposits made at the start or the end of the month?
The end. A deposit does not earn interest in the month it is added. The SIP calculator assumes the start of the month, which is why those two pages disagree on identical inputs.
Can the starting amount or the monthly deposit be zero?
Yes. Zero monthly deposit is ordinary compound growth of a lump sum. Zero starting balance is an ordinary annuity. Both are in the worked examples.
Is this APR, APY, or a return after inflation?
It is a nominal annual rate, divided by 12. It is not an APY, and it is not reduced for inflation, fees, or tax. A brokerage that disagrees is often using one of those, or a deposit on a different day.
Why doesn’t the chart match my account to the cent?
The chart plots this constant-rate formula at each year-end. Real accounts post interest on their own calendar and may skip weekends. Use the figure to compare scenarios, not to audit a statement.