Sprint 5 Showcase
Compound Interest Calculator
Precision calculations powered by BigNumber with a yearly growth chart to compare invested capital vs compounded growth.
Future Value
$263,122.95
Total Invested
$70,000.00
Compounded Gain
$193,122.95
Final value is 26.31x your starting principal over 20 years.
Projection chart
240 compounding periods simulated
How it works
The Compound Interest Calculator computes the future value of an investment or savings deposit over time, accounting for periodic compounding of earned interest. Enter the principal amount, annual interest rate, compounding frequency (daily, monthly, quarterly, annually), and time period — and the calculator shows the total amount, total interest earned, and a year-by-year growth table.
Compound interest is the mechanism that makes long-term saving and investing powerful — and long-term debt dangerous. Einstein (apocryphally) called it the "eighth wonder of the world." This calculator makes the math visible: at 7% annual return, a $10,000 investment compounding monthly becomes $20,097 in 10 years and $76,123 in 30 years. The same money in a simple interest account earns only $17,000 in 10 years.
How to use it: enter the principal (starting amount), annual interest rate (%), compounding frequency, and investment period in years. Optional: enter monthly contributions (for savings plans, recurring deposits, or systematic investment plans). Click Calculate.
Results shown: - Final balance: total value at the end of the period - Total interest earned: the amount added by compounding - Interest-to-principal ratio: how much of the final balance is growth vs. original investment - Year-by-year table: balance at the end of each year - Growth chart: visual representation of compound growth curve
Compounding frequency effect: more frequent compounding produces higher returns. Monthly compounding on a 5% annual rate produces an effective annual rate (EAR) of 5.116%. Daily compounding produces 5.127%. The difference is small at low rates and short periods but becomes meaningful at higher rates and longer time horizons.
Formula: A = P(1 + r/n)^(nt) where P = principal, r = annual rate, n = compounding periods per year, t = years.
Privacy: all calculations run in the browser. No financial data is transmitted.
Frequently Asked Questions
- More frequent compounding always produces more interest. Daily compounding > monthly > quarterly > annually. However, the difference is smaller than most people expect: $10,000 at 5% for 10 years compounded annually = $16,289; compounded daily = $16,487 — a difference of only $198. The rate matters far more than the compounding frequency.
- Enter your current balance as the Principal, your savings account's APY as the Annual Rate, select your account's compounding frequency (most savings accounts compound daily), enter your investment period in years, and add your monthly deposit amount if you make regular contributions. The result shows your projected balance.
- The Rule of 72 is a quick mental calculation: divide 72 by your annual interest rate to estimate how many years it takes to double your money. At 6% annual return, 72 ÷ 6 = 12 years to double. This is an approximation of the compound interest doubling formula t = ln(2)/ln(1+r).
- Yes. Enter 0 as the principal (or your existing investment as principal), enter your monthly contribution amount in the Monthly Contribution field, enter the expected annual return, and set the period. The calculator shows the final corpus — the total value of all contributions plus compound growth.