💵 Interest Calculator

Principal ($)

Annual Rate (%)

Time (Years)

Principal ($)

Annual Rate (%)

Time (Years)

Compound Frequency

What is the Interest Calculator?

The Interest Calculator works out how much interest a sum of money earns or owes over time, using either simple or compound interest. Simple interest applies a flat rate to the original principal each year; compound interest applies the rate to the principal plus all interest already accumulated, so it grows faster the longer money sits.

How to Use It

Choose the Simple Interest tab and enter your principal, annual rate, and time in years to see the interest earned and total amount. For Compound Interest, also select how often interest compounds — daily, monthly, quarterly, or annually — and the tool shows the interest earned, total amount, and how much more you gain compared to simple interest at the same rate.

When to Use It

Use Simple Interest for quick estimates on short-term loans or basic interest problems, and Compound Interest for savings accounts, CDs, or any account or debt where interest compounds. Comparing the two also shows why compounding frequency matters — daily compounding earns slightly more than annual compounding at the same stated rate.

Who Benefits

Savers comparing account offers, borrowers evaluating loan terms, and students learning the difference between simple and compound interest formulas can all use this to see the numbers side by side instead of computing them by hand.

Frequently Asked Questions

Simple interest is calculated only on the original principal: Interest = P × r × t. Compound interest is calculated on the principal plus accumulated interest, so it grows exponentially over time. For savings, compound is better for you; for debt, simple is better.

Simple Interest = Principal × Rate × Time. Example: $10,000 at 5% for 3 years = $10,000 × 0.05 × 3 = $1,500 in interest. Total amount = $11,500. Simple interest is commonly used for short-term loans, car loans, and some personal loans.

A = P(1 + r/n)^(nt), where A is the final amount, P is principal, r is annual rate, n is compounding frequency per year, and t is years. More frequent compounding (daily vs annually) produces slightly more interest due to the compounding effect.

💵 Interest Calculator