Compound Interest Calculator

What this compound interest calculator does

This English-language compound interest calculator lets you figure compound interest growth across any time horizon — from a single lump sum to a plan with regular monthly or annual contributions. Enter your principal, annual rate, term in years, and compounding frequency (annually through daily), and the tool computes a final balance plus a year-by-year breakdown of principal, cumulative contributions, and interest earned. One thing worth knowing upfront: the final balance shown is pre-tax and pre-inflation. Nominal interest rates don't account for what inflation quietly removes — historically around 2–4% per year in the US — or the tax drag on interest income in taxable accounts. For a quick sanity check, the rule of 72 is handy: divide 72 by your annual rate to estimate how many years it takes to double your money. 100% client-side — your data never leaves your browser. No uploads, no tracking, no server logs.

Features

• Six compounding frequencies. Choose annually, semi-annually, quarterly, monthly, weekly, or daily compounding. Frequency matters more in the early years and for shorter terms where the difference between monthly and daily is still meaningful.
• Periodic contributions with timing control. Add a fixed contribution per period and specify whether it lands at the beginning or end of each period. Beginning-of-period contributions earn one extra full period of interest, which adds up noticeably over long horizons.
• Year-by-year breakdown table. Toggle a detailed table showing start balance, contributions made that year, interest earned, and end balance for every year. Useful for spotting exactly when interest starts outpacing contributions.
• Three-card summary. At a glance, see your original principal, total contributions made over the term, and total interest earned separately — so you know precisely how much growth came from saving versus compounding.
• Rule of 72 reference. The calculator surfaces how the rule of 72 applies to your inputs, giving you a quick mental model to cross-check the result before trusting the full projection.
• No server, no account required. All arithmetic runs locally in your browser using standard JavaScript math. No data is transmitted; you can even use it offline after the page loads. Compare this to cloud-based tools where your financial inputs are logged.

How to use the compound interest calculator

Fill in the four core fields, optionally add a contribution, then read the summary cards or expand the year-by-year table.

1. Enter your principal. Type the starting balance — this is the lump sum you're beginning with, such as $10,000 in an index fund or a high-yield savings account.
2. Set annual rate and term. Enter the nominal annual interest rate (e.g., 7 for 7%) and the number of years. Remember this is the nominal rate — real purchasing-power growth subtracts inflation on top.
3. Pick a compounding frequency. Select how often interest compounds. Most savings accounts and bonds compound monthly; many index funds are modeled annually. Selecting daily gives the theoretical maximum for a given nominal rate.
4. Add optional periodic contributions. If you plan to save regularly — say, $500/month into a 401(k) — enter that amount and choose whether contributions land at the beginning or end of each period. Beginning-of-period is typical for automatic payroll deductions.
5. Read the results and expand the table. The three summary cards show principal, total contributions, and interest earned. Click 'Show year-by-year breakdown' to see how the balance evolves annually — helpful when presenting a savings plan to clients or a financial advisor.

Common use cases

• Retirement savings projection. Model monthly 401(k) or IRA contributions over 30 years to estimate how much you might accumulate by retirement age. A Chicago-based worker maxing out contributions at $23,000/year starting at 35 can use this to visualize the gap a 10-year delay creates — a powerful argument for starting early.
• College fund planning. Plan a 529 account over an 18-year horizon from a child's birth. Enter the initial deposit, expected average return, and monthly contributions to see whether you're on track for a New York tuition estimate — and how cumulative interest reduces how much you personally need to save.
• Comparing savings vehicles. Run the same principal and term twice — once at a high-yield savings rate (e.g., 4.8%) and once at a long-run index fund assumption (e.g., 7%) — to see the divergence in terminal balance. Pair this with the [CAGR Calculator](/en/cagr-calculator/) if you already know a historical ending value and want to reverse-engineer the annualized rate.
• Demonstrating the cost of waiting. One extra lump-sum payment early in a loan or investment term can have an outsized effect. Saving $12,000 today at 6% over 25 years produces far more than saving $12,000 in year 10 — and a similar logic explains why a one-time extra mortgage payment can eliminate tens of thousands in cumulative interest. For the borrowing side of that comparison, the [loan calculator](/en/loan-calculator/) handles amortization schedules.
• Teaching compounding to students or clients. The year-by-year table makes it easy to show exactly when interest income overtakes annual contributions — the 'crossover point' that makes compounding intuitive rather than abstract. Useful for financial literacy workshops or onboarding new investors.

Frequently asked questions