Calculate to see the future value, contributions, and interest together with the growth chart.
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Free Compound Interest Calculator
Use this free compound interest calculator to see exactly how your savings and investments grow over time. Enter a starting balance, an interest rate, and optional monthly contributions, and the tool projects your future value year by year with an interactive chart. Whether you are planning for retirement, building an emergency fund, comparing a high-yield savings account against an index fund, or running a "what if" on a one-time deposit, you get accurate numbers in seconds — and every calculation runs entirely in your browser.
Unlike a simple savings calculator, this one models regular contributions, compounding frequency (daily, monthly, quarterly, or annually), inflation, and tax on interest — so the projection reflects what you would realistically keep, not just a headline number.
How to Use the Calculator
Enter your initial investment (starting principal).
Set the annual interest rate and how often interest compounds.
Add a regular contribution — monthly, bi-weekly, weekly, or annually.
Optionally expand Advanced Options to adjust for inflation and tax.
Click Calculate to see your projected growth, chart, and year-by-year table.
The Compound Interest Formula
Compound interest is calculated with the formula A = P(1 + r/n)nt, where:
A — the future value (your final balance)
P — the principal (your starting amount)
r — the annual interest rate as a decimal (7% = 0.07)
n — how many times interest compounds per year
t — the number of years
For regular deposits, this calculator spreads the annual contribution total across the compounding periods and adds each portion after that period’s interest. Monthly contributions with monthly compounding therefore represent end-of-month deposits; other frequency combinations are an approximation of deposit timing. To learn how this differs from a flat interest rate, read our guide on compound vs. simple interest.
A Worked Example
Start with $10,000, assume a constant 7% nominal annual rate compounded monthly, and add $200 at the end of each month for 30 years. With tax and inflation set to zero and no fees, the final balance is $325,159: $82,000 contributed and $243,159 interest, rounded to whole dollars. At 40 years, the same assumptions give $688,077. These are mathematical projections, not guaranteed investment returns. Our guide to starting early compares the effect of different saving timelines.
Common Use Cases
Retirement planning — project a 401(k), IRA, or pension pot over decades.
Savings goals — work out how long it takes to reach a house deposit or college fund.
Comparing accounts — pit a high-yield savings APY against an index-fund return.
Debt awareness — see how the same math works against you on a credit-card balance.
FIRE planning — model aggressive contributions toward financial independence.
Features
Regular contributions — Model monthly, weekly, or annual deposits
Inflation adjustment — See your returns in real purchasing power
Tax impact — Factor in tax rates on interest income
Interactive chart — Visualize growth of principal vs. interest
Year-by-year breakdown — Detailed table of balances over time
Export results — Download as CSV or JSON
Client-side calculations — Inputs and results stay in your browser
The Power of Compound Interest
Compound interest is often described as interest earning interest. Starting early and contributing regularly are two powerful factors because each period's gains can become part of the balance used for future growth. A fast way to feel the effect is the Rule of 72: divide 72 by your rate to estimate how many years it takes your money to double. For a deeper walkthrough of the mechanics, see how compound interest works.
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest, which is only calculated on the principal, compound interest grows exponentially over time — making it one of the most powerful concepts in finance.
How is compound interest calculated?
The formula is A = P(1 + r/n)^(nt), where P is the principal, r is the annual interest rate, n is the number of times interest is compounded per year, and t is the number of years. Our calculator also accounts for regular contributions and inflation adjustments.
What is the difference between APR and APY?
APR (Annual Percentage Rate) is the stated interest rate without accounting for compounding. APY (Annual Percentage Yield) includes the effect of compounding and represents the actual annual return. APY is always equal to or higher than APR.
How often should interest be compounded?
More frequent compounding yields slightly higher returns. Daily compounding earns more than monthly, which earns more than annually. However, the difference between daily and monthly compounding is usually minimal for most savings accounts.
How does inflation affect my savings?
Inflation reduces the purchasing power of your money over time. Our calculator lets you toggle inflation adjustment to see your returns in "real" (inflation-adjusted) terms. A 7% return with 3% inflation gives approximately 4% real growth.
Is my financial data stored?
No. Calculation inputs and results stay in your browser and are not sent to our servers. The site may still use analytics or advertising cookies as described in the privacy policy.
What is the Rule of 72?
The Rule of 72 is a quick way to estimate how long it takes to double your money. Divide 72 by your annual interest rate. For example, at 8% interest, your money doubles in approximately 72 ÷ 8 = 9 years.