Compound Interest Calculator
See how an investment or loan grows over time with compound interest, using the formula A = P(1 + r/n)^(nt). Enter the principal, annual rate, compounding frequency and term in years, and the calculator returns the future value plus the interest earned. An easy way to put the power of compounding to work — privately, in your browser.
What is compound interest?
Compound interest is interest calculated on both the money you originally invested — the principal — and on the interest that has already accumulated. That is the key difference from simple interest, which pays only on the original amount. Because the interest earns its own interest, growth speeds up over time, so a sum left to compound can become far larger than the same money at simple interest. The standard formula is A = P(1 + r/n)^(nt), where A is the future value, P the principal, r the annual rate, n the number of compounding periods per year and t the time in years. How often interest is compounded matters: monthly compounding earns more than annual, and daily compounding earns more still, because each period adds to the base the next is calculated on. Compound interest drives the growth of savings accounts, fixed deposits and index funds, and it also works in reverse on loans and credit card debt — which is why understanding it pays off.
Example
Invest $1,000 at 5% a year, compounded monthly, for 10 years. The calculator returns a future value of $1,647.01, so you earned $647.01 in interest — more than the $500 that simple interest would have paid over the same term.
Who is this compound interest calculator for?
Compound interest rewards time, so it matters most to people saving or investing for a goal. It is useful for four kinds of users.
- Students and young adults: starting early is the single biggest advantage. A student using the compound interest calculator for students can see how a small monthly habit grows — and why a few years of head start beat a higher amount saved later.
- Couples: planning a home, a family or a shared retirement goal, a couple can run the compound interest calculator for couples to project what joint savings become over time and set a realistic deposit amount.
- Salaried professionals: with a regular salary to invest, the compound interest calculator shows how contributions plus compounding compound into a substantial long-term balance.
- Retirees: for retirees, a compound interest calculator for retirees illustrates how an existing nest egg keeps compounding — and how slowing growth in inflation-adjusted terms can reduce future buying power.
Compound interest by time period
This table shows how $1,000 at 5% a year, compounded monthly, grows over different terms — the same setup as the calculator above. Notice how the interest earned accelerates as time lengthens.
| Term (years) | Future value | Interest earned |
|---|---|---|
| 1 | $1,051.16 | $51.16 |
| 5 | $1,283.36 | $283.36 |
| 10 | $1,647.01 | $647.01 |
| 20 | $2,712.64 | $1,712.64 |
| 30 | $4,467.74 | $3,467.74 |
Common use cases
- Projecting how a savings account or fixed deposit will grow.
- Comparing returns at different compounding frequencies.
- Seeing what a long-term goal needs to accumulate.
- Understanding the true cost of borrowing on a loan or card.
Pro tips
- More frequent compounding earns more interest; daily beats monthly at the same rate.
- Time is the biggest factor — the earlier you start, the more compounding works.
- The Rule of 72 estimates doubling time: 72 ÷ rate gives the years to double.
- Compare the same rate and term across options to choose the best compounding frequency.
How to use
- Enter the principal amount you start with.
- Set the annual interest rate and how often it compounds.
- Enter the number of years, then click Calculate to see the future value and total interest earned.
Compound Interest Calculator FAQs
What is compound interest?
Compound interest earns interest on both the original principal and on previously earned interest, so money grows faster over time.
How is compound interest calculated?
Use A = P(1 + r/n)^(nt), where P is the principal, r the annual rate, n the compounding periods per year and t is time in years.
Does compounding frequency affect interest?
Yes. The more often interest is compounded, the more you earn, because each new period is calculated on a larger base.
What is the difference between compound and simple interest?
Simple interest pays only on the original principal. Compound interest pays on the principal plus the interest built up, so it grows faster.
What is future value?
Future value is the total amount an investment is worth at the end of the term, including all the interest earned.
What is the Rule of 72?
The Rule of 72 estimates how long money takes to double: divide 72 by the annual interest rate. At 6%, that is about 12 years.
How does compounding frequency change the result?
Daily compounding can beat monthly and annual at the same rate because interest is added to the base far more often.
Does compound interest apply to loans too?
Yes. Loans and credit cards charge compound interest, which is why unpaid balances can grow quickly.
What is the best compounding frequency for savings?
For the same stated rate, more frequent compounding — like daily or monthly — gives a slightly higher effective return.
Is this compound interest calculator free and private?
Yes. It is free, runs in your browser, and nothing is uploaded.
More FAQs
Is this calculator free?
Yes, it is completely free with no signup and no limits.
Does it run in my browser?
Yes. Everything is calculated locally on your device — nothing is uploaded.
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