Compound Interest Calculator
See how savings grow over time.
Your savings plan
More options: tax, inflation and yearly step-up
Compound Interest Calculator Math Formula
Compound interest means you earn interest on your money and on the interest it already earned. Here is the formula the calculator uses, followed by a worked example with real numbers.
The formula
r = Yearly rate ÷ 12
n = Years × 12
Starting money growth = P × (1 + r)n
Deposits growth = D × [((1 + r)n − 1) ÷ r]
Final amount = Starting money growth + Deposits growth
Interest earned = Final amount − (P + D × n)
- P = starting money
- D = monthly deposit
- r = monthly interest rate
- n = total number of months
Now let's work through it step by step with one simple example: 10,000 to start (P), 500 added every month (D), 8% yearly interest, for 10 years.
Step 1: Your starting money grows
Interest is added every month. Divide the yearly rate by 12 to get the monthly rate, then let it multiply your money once for each month.
Monthly rate = 8% ÷ 12 = 0.6667%
10,000 × (1 + 0.006667)120 = 10,000 × 2.2196 = 22,196.40
10 years is 10 × 12 = 120 months, so the growth factor is applied 120 times. Your 10,000 grows to 22,196.40 without adding anything.
Step 2: Your monthly deposits grow
Each deposit is added at the end of its month and starts earning interest from the next month, so early deposits grow the most. The calculator adds them all up with this shortcut:
500 × [(2.2196 − 1) ÷ 0.006667] = 91,473.02
You put in 500 × 120 = 60,000, and it grows to 91,473.02.
Step 3: Add it all up
Final amount = 22,196.40 + 91,473.02 = 113,669.42
You put in = 10,000 + 60,000 = 70,000
Interest earned = 113,669.42 − 70,000 = 43,669.42
More than half of your final amount is interest you did not have to deposit.
Step 4: How long to double your money?
A quick shortcut is the Rule of 72: divide 72 by the yearly rate.
72 ÷ 8 = 9 years
The exact answer for 8% compounded monthly is 8.7 years. Because of monthly compounding, you really earn 8.30% a year, a little more than 8%.
Step 5: Tax, inflation and yearly increase
Tax. If 20% of your interest goes to tax, only the rest keeps compounding.
8% × (1 − 0.2) = 6.4% a year
Inflation. Prices rise, so future money buys less. With 3% inflation, divide the final amount by the price rise over 10 years.
113,669.42 ÷ 1.3439 = 84,580.72 in today's money
Yearly increase. If you raise your deposit by 5% each year, it goes from 500 to 525 in year 2 and 551.25 in year 3.
Online Compound Interest Calculator
Our free online compound interest calculator shows how your savings or investment grow when the interest you earn is added back to your balance and starts earning interest too. Enter a starting amount, an optional monthly deposit, the interest rate and the number of years, and you get the final balance, the total interest earned and a year-by-year growth chart in seconds. It works with any compounding frequency, from daily and monthly to quarterly and yearly.
Use it as a simple calculator for any rate, or switch to the country-wise version to plan with real fixed deposit, savings account and government scheme rates for India, the United States, the United Kingdom, Canada, Australia and more. It is useful for comparing banks, estimating the maturity value of a deposit, planning a retirement or education fund, or simply seeing why starting early and staying invested makes such a big difference over time. It runs in your browser, needs no sign-up and works on phones, tablets and desktops.
Features Of ToolVaya Compound Interest Calculator
- Daily, monthly, quarterly, half-yearly or yearly compounding
- Starting amount and monthly deposits
- Country-wise FD, savings and government scheme rates
- Compare banks and schemes side by side
- Year-by-year growth chart
- Detailed yearly breakdown table
- Download a PDF report and share your result
- Free, no sign-up, works on phone, tablet and desktop
- Private: calculated in your browser, nothing is stored
Compound interest calculator with real government schemes and bank rates
About this tool
Pick a country, then a government scheme or a bank, and the current rate, compounding and tax treatment are filled in for you. Enter what you save and for how long to see what it grows to, how much of it is interest and what it is worth in today's money.
How the rates stay up to date
- Live policy rates. For India, the US, the UK, Canada and Australia the tool reads the central bank rate from the Bank for International Settlements every 30 minutes. Bank products that follow it move automatically, as an estimate based on how much of a rate change banks usually pass on.
- Government schemes are fixed by notification, usually every quarter. Each one shows the date it was published and a review due flag once the next revision date passes, with a link to the official source.
- Smart checks. Yearly deposit limits, lock-in periods and product terms are checked against your plan, and the ranking shows which option wins for your exact numbers.
Good to know
Rates are for information only and can change. Deposits are assumed at the end of each month, and interest on products that pay out is assumed to be reinvested. Always confirm the rate and rules with the scheme or bank before you commit, and treat tax figures as a simple estimate.