Compound Interest Calculator
Calculate how your investment or savings grows over time with the power of compounding.
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How to use this calculator
A = final amount, P = principal, r = annual interest rate (decimal), n = compounding frequency per year, t = time in years.
- 1
Enter the principal — the amount you are investing or depositing today.
- 2
Enter the annual interest rate offered by your savings account or investment.
- 3
Set the time period in years you want to project.
- 4
Choose the compounding frequency — monthly is standard for most savings accounts.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the principal. Compound interest is calculated on the principal plus all previously earned interest, so your money grows faster over time.
How does compounding frequency affect my returns?
The more frequently interest compounds, the more you earn. Daily compounding yields slightly more than monthly, which yields more than annual. For long time horizons, the difference becomes meaningful.
What is the Rule of 72?
Divide 72 by your annual interest rate to estimate how many years it takes for your money to double. At 8% interest, your money doubles in roughly 72 ÷ 8 = 9 years.
Can I use this calculator for a savings account?
Yes. Enter your starting deposit as the principal, your account's APY as the rate, and choose monthly compounding (most common for savings accounts).
What is compound interest?
How to use the compound interest
This compound interest gives you instant, accurate results — no registration or download required. Enter your values above and get your result in seconds. The tool is free, works on all devices, and keeps your data private — nothing is stored or shared.
How the compound interest works
The compound interest uses standard formulas used in financial planning, budgeting, and investment decisions. Enter your inputs, and the tool calculates the result instantly in your browser. No server-side processing means your data stays on your device. Results update in real time as you change inputs.
How compound interest works
Compound interest is the process by which interest earned on a principal amount is reinvested, so that subsequent interest applies to the accumulated total rather than the original deposit alone. This creates exponential rather than linear growth — the longer money remains invested, the more powerful the effect becomes.
Compound vs simple interest — a real example
On a $10,000 deposit at 8% over 5 years, simple interest returns $14,000. Compound interest (monthly) returns $14,898 — a $898 advantage that grows larger with time. Over 20 years, the same comparison produces a difference of more than $26,000.
Where compound interest applies in everyday finance
Compound interest applies to savings accounts, certificates of deposit (CDs), bonds, money market accounts, and retirement vehicles like 401(k) and IRA plans. Credit card debt also compounds, usually daily — making it important to pay balances in full each month.
Compound interest: how it works
This free tool helps you plan and compare financial scenarios in seconds. Enter your figures, adjust the assumptions, and instantly see how different inputs affect the outcome — ideal for budgeting, benchmarking, and data-driven decision-making.
Who uses this tool?
Financial planners, accountants, students, and individuals use it to model scenarios before committing to major financial decisions. It is equally useful for quick sanity checks and detailed what-if analyses.
Learn more from an authoritative source:
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →