Compound Interest Calculator
See how a lump sum and regular deposits grow over time, with any compounding and any currency.
- Calculated in your browser
- Formula and rounding
- Reviewed
Final balanceExample
$47,526.55
after 10 years
- Paid in$34,000.0072%
- Interest earned$13,526.5528%
- Total paid in
- $34,000.00
- Total interest
- $13,526.55
- Effective annual rate
- 5.116%
Effective annual rate
EAR = (1 + r/m)^m − 1r = 0.05rateType = nominalcompounding = monthly
= 0.05116189…
Convert the annual rate to a rate per month
i = r / pr = 0.05p = 12rateType = nominalm = 12
= 0.00416666…
Regular contribution per monthly period (end of period)
CC = 200g = 0
= 200
Final balance: each step adds interest at the per-step rate and the contribution
B_k = B_(k−1) × (1 + i) + Cinitial = 10000i = 0.00416666…steps = 120
= 47526.55
Total paid in
initial + Σ contributionsinitial = 10000
= 34000
Total interest (after tax on growth, if any)
final − total paid infinal = 47526.55paidIn = 34000
= 13526.55
Final balance in today's money
real = final ÷ (1 + inflation)^yearsfinal = 47526.55inflation = 0years = 10
= 47526.55
- Paid in
- Interest
After 10 years, the balance is $47,526.55: $34,000.00 paid in and $13,526.55 interest.
Assumptions
- Rate is a nominal annual rate of 5% compounded monthly.
- Interest is credited monthly at the equivalent rate of the stated rate.
- Contributions are made at the end of each monthly period.
- Growth is not taxed (tax-free account or tax not modelled).
- Real values assume constant inflation of 0% a year.
- Fees and charges are not modelled.
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Estimates for general information only — not financial, tax or legal advice. Your actual figures depend on your employer’s payroll, your full tax situation, your lender’s or bank’s terms and rules we may not model. Check official sources and speak to a qualified adviser before making decisions. Disclaimer · Report an error
How to calculate compound interest with monthly contributions
Compound interest is interest earned on interest. Each period, the interest is added to your balance, and the next period’s interest is worked out on that bigger balance. Over a few years the effect is small. Over decades it can be larger than everything you paid in.
This calculator shows that growth step by step. Enter a starting amount, any regular deposits, the rate and how long the money stays put. You get the final balance, how much of it came from you and how much came from interest, and a schedule you can check line by line. It works in any currency, so it fits a savings account in pounds, a deposit in euros or an investment in dollars.
- 1
Enter what you start with and what you add
Type your starting deposit, then any regular contribution and how often you make it. Choose whether each deposit lands at the start or the end of the period, and add a yearly increase if your deposits will grow.
- 2
Set the rate the way your bank quotes it
Pick “effective annual” if the rate is shown as AER, APY or EAR. Pick “nominal” if it is a headline rate with a stated compounding, then choose daily, monthly, quarterly, semi-annual, annual or continuous.
- 3
Choose the term and read the results
Set the years and months. The result shows the final balance, your total contributions and the total interest. Add an inflation rate to see the balance in today’s money, then open the schedule or download it as CSV.
What this calculator does
- Starting deposit plus weekly, monthly, quarterly or yearly contributions
- Contributions at the start or end of each period
- Yearly increase in contributions of up to 20%
- Effective annual rate (AER, APY, EAR) or nominal rate
- Daily, monthly, quarterly, semi-annual, annual or continuous compounding
- Final balance, total contributions and total interest
- Inflation-adjusted real value of the final balance
- Growth chart, yearly or monthly schedule and CSV export
Worked example: 10,000 at 5% for 10 years
Same rate, different compounding
You put 10,000 (any currency) into an account paying a nominal 5% a year and leave it for 10 years with no further deposits.
| Compounding | Final balance | Interest earned |
|---|---|---|
| Annual | 16,288.95 | 6,288.95 |
| Monthly | 16,470.09 | 6,470.09 |
Monthly compounding adds 181.14 more in this scenario, only because interest is credited more often. Now add regular saving: starting from 0, deposit 100 at the end of each month for 10 years at 5% nominal, compounded monthly. You pay in 12,000 and finish with 15,528.23. Move the deposits to the start of each month and the total is 15,592.93, because every deposit earns one extra month of interest.
How it’s calculated
For a single deposit, the balance after n periods is P × (1 + i)^n, where P is the starting amount and i is the rate per period. With a nominal annual rate r compounded m times a year, i = r ÷ m. So 5% compounded monthly is 0.05 ÷ 12 each month.
Regular deposits made at the end of each period add D × ((1 + i)^n − 1) ÷ i. Deposits at the start of the period earn one extra period, so that figure is multiplied by (1 + i). Continuous compounding uses P × e^(r × t).
When you choose an effective annual rate, the calculator converts it to a per-period rate with (1 + AER)^(1/12) − 1 for monthly steps. That way a single 10,000 deposit at 5% effective grows to exactly 10,500.00 in one year, which is what an AER promises. The schedule rounds to your currency’s smallest unit at each step. You can read the full method on our methodology page.
AER and APY vs nominal rates
Banks quote savings rates in two ways. A nominal (or gross) rate is the headline figure before compounding. An effective annual rate already includes compounding: in the UK it is called AER, in the US APY, and elsewhere EAR. A nominal 5% compounded monthly works out to an effective rate of about 5.12%.
Mixing them up makes a small but real difference over long terms, so the calculator asks which one you have. Our guide to APR, AER, APY and nominal rates walks through the conversions with examples.
Related calculations
If you know the amount you want and need the monthly deposit, the savings goal calculator solves it backward. To see what a future balance may buy, compare it with past price changes in the inflation calculator. Compound interest also works against you when you borrow, which the loan calculator shows in its amortization schedule. If you are weighing saving against paying down a home loan, see overpay the mortgage or save.
Good to know
- Results assume the rate stays the same for the whole term. Real savings rates change, and investment returns go up and down and can be negative.
- Tax on interest or growth is not deducted unless you enter it. Rules differ by country and by account type.
- The real value uses one constant inflation rate. Actual inflation varies from year to year.
- Fees, minimum balances and bonus rates that expire are not modelled. Check your account terms for those.
What happens to the numbers you type
Your numbers stay in your browser. MoneyOtter works out your results on your device. We don’t send the amounts you type to our servers or store them. If you allow analytics, we record only broad ranges (for example “middle tax band”) to understand how the calculators are used. Like any website with ads, this page also loads advertising scripts; see our Privacy Policy.
The calculator is plain code running in this tab. It makes no network requests with your figures, and nothing is saved when you leave unless you choose to keep it. Read the privacy policy for how ads and analytics work on this site.
Related calculators and guides
Questions people ask
How do I calculate compound interest with monthly contributions?
Add the growth of the starting amount, P × (1 + i)^n, to the growth of the deposits, D × ((1 + i)^n − 1) ÷ i, where i is the monthly rate and n the number of months. The calculator does both and shows each month in the schedule.
Is monthly or annual compounding better for savers?
At the same nominal rate, more frequent compounding pays slightly more. In the worked example, 10,000 at 5% for 10 years ends at 16,470.09 with monthly compounding and 16,288.95 with annual compounding. If two accounts both quote an AER, the compounding is already included, so compare the AERs directly.
What is the difference between AER, APY and the interest rate?
AER (UK) and APY (US) are effective annual rates that include compounding. A nominal or gross rate does not. A nominal 5% compounded monthly equals an AER or APY of about 5.12%.
Does it matter if I pay in at the start or end of the month?
Yes, a little. A deposit at the start of the month earns interest for that month. Saving 100 a month for 10 years at 5% gives 15,592.93 with start-of-month deposits and 15,528.23 with end-of-month deposits.
What does “real value” mean in the results?
It is the final balance expressed in today’s money, using the inflation rate you enter. It shows roughly what the balance could buy at today’s prices.
Can I use this calculator for investments as well as savings?
Yes, as long as you treat the rate as an assumed average. Investment returns are not fixed, so the result is an illustration of one steady path, not a forecast.
What happens if I enter a rate of 0%?
The final balance equals your starting amount plus the exact sum of your contributions, with no interest added.
Sources and review
- Investor.gov (US SEC) — Compound interest calculator
- Investor.gov (US SEC) — What is compound interest?
- European Central Bank — What is inflation?
Estimates for general information only — not financial, tax or legal advice. Your actual figures depend on your employer’s payroll, your full tax situation, your lender’s or bank’s terms and rules we may not model. Check official sources and speak to a qualified adviser before making decisions.
Page reviewed by the MoneyOtter team · Methodology · Changelog · Report an error