Compound Interest Calculator (2026) - Final Amount & EAR

Compounding turns rate into a final balance

Simple interest grows linearly. Compound interest reinvests each period's earnings, so growth accelerates. This page applies a fixed nominal annual rate at the frequency you choose for the full year count.

Defaults: $10,000 principal, 7% annual rate, 10 years, monthly compounding (12x per year). Final = 10,000 x (1 + 0.07/12)^(120) = $20,096.61. Interest earned = $10,096.61. Effective annual rate = 7.23%.

Principal must be greater than 0. Rate 0% means final equals principal and interest is $0.

Frequency, loans, and runway

Savings accounts often compound daily; bonds may pay semi-annually. Change the dropdown to match the product you are comparing. Daily vs monthly on 7% over 10 years is a few hundred dollars on $10k, not double.

Borrowing uses the same math in reverse. The Simple Loan EMI Calculator shows payment on a loan; this page shows growth on cash you keep.

Founders modeling idle treasury before burn picks up use the Startup Runway Calculator for cash-out dates, not compound growth alone.

Copy and compare scenarios

Copy exports principal, rate, years, frequency label, final amount, interest, and EAR. Paste two scenarios side by side (5 vs 10 years, monthly vs annual) before you move money.

Inflation and tax are omitted. A 7% nominal return with 3% inflation is not 7% real. Put after-tax final in manually if you know the rate.

Statements with deposits, dividends taken as cash, or variable returns belong in the ROI Calculator as start and end balances instead.

Frequently Asked Questions (FAQ)

What is the compound interest formula used here?

Final amount = P x (1 + r/n)^(n x t), where P is principal, r is annual rate as a decimal, n is compounds per year, and t is years. Interest earned = final - P. Effective annual rate = (1 + r/n)^n - 1. Defaults: $10,000, 7%, 10 years, monthly: final $20,096.61, interest $10,096.61, EAR 7.23%.

Why does compound frequency matter?

More compounding periods per year yield a higher effective rate at the same nominal APR. Monthly compounding at 7% nominal gives 7.23% EAR; annual compounding at 7% gives exactly 7% EAR. The dropdown sets n.

Are monthly contributions included?

No. One lump principal, fixed rate, fixed years. Regular deposits need a different model or spreadsheet. Use this for "what if I leave X alone at Y% for Z years."

How does this relate to ROI?

ROI on this site compares two dollar amounts over time (simple and CAGR). Compound interest fixes rate and frequency instead of a final value. Use the ROI Calculator when you already know start and end balances from statements.

Compound Interest Calculator