Interest Calculator

Calculate simple and compound interest on savings or loans.

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Loan Amount

Annual Interest Rate (%)

Term (Months)

Monthly Payment

$188.71

Total Interest

$1,322.74

Total Cost

$11,322.74

Principal (88%)Interest (12%)

$10,000.00$1,322.74

Amortization Over Time

Amortization Schedule

Month	Payment	Principal	Interest	Balance
1	$188.71	$147.05	$41.67	$9,852.95
2	$188.71	$147.66	$41.05	$9,705.30
3	$188.71	$148.27	$40.44	$9,557.02
4	$188.71	$148.89	$39.82	$9,408.13
5	$188.71	$149.51	$39.20	$9,258.62
6	$188.71	$150.13	$38.58	$9,108.48
7	$188.71	$150.76	$37.95	$8,957.72
8	$188.71	$151.39	$37.32	$8,806.34
9	$188.71	$152.02	$36.69	$8,654.32
10	$188.71	$152.65	$36.06	$8,501.66
11	$188.71	$153.29	$35.42	$8,348.37
12	$188.71	$153.93	$34.78	$8,194.45

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What is Interest Calculator?

An interest calculator computes the total interest earned or paid on a sum of money, using either simple interest (principal × rate × time) or compound interest (where earned interest is added to the principal and earns interest itself). The difference between the two is dramatic over time. Compound frequency — daily, monthly, quarterly, or annually — determines how often interest is added to the balance. APY (Annual Percentage Yield) measures the true annual return after compounding, while APR (Annual Percentage Rate) is the nominal rate before compounding. Savings accounts and certificates of deposit (CDs) typically use compound interest; simple interest is more common in short-term personal loans and some auto loans.

How to use

Enter the principal amount — the starting balance or loan amount.
Input the annual interest rate as a percentage (e.g., 5 for 5%).
Enter the time period in years (or months if the calculator supports it).
Select the compound frequency: daily, monthly, quarterly, or annually. Leave on simple interest to compare.
Click Calculate to see total interest earned or paid, plus the ending balance.
Toggle between compound frequencies to see how daily compounding compares to monthly on the same rate.

Why it matters

The difference between simple and compound interest is enormous over time. A $10,000 investment at 5% simple interest over 10 years earns $5,000 in interest. The same amount at 5% compounded monthly earns approximately $6,470 — a 29% difference — with no additional contributions. Compound frequency also matters when comparing savings accounts: two accounts both advertised at 4.80% APR can yield meaningfully different APYs depending on how often they compound. This calculator also helps evaluate financing offers — comparing whether a 0% promotional loan actually beats a cash purchase discount when the time value of money is considered.

Pro tip

When comparing savings accounts or CDs, always look at APY — not APR. APY accounts for compounding and shows your true annual return. A savings account at 5.00% APR compounded daily yields an APY of approximately 5.13%, while the same rate compounded annually yields exactly 5.00%. The difference grows as balances grow. Banks are required to disclose APY, so use that number for apples-to-apples comparisons.

Frequently Asked Questions

Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus previously earned interest, growing faster over time.

Interest can be compounded daily, monthly, quarterly, or annually. More frequent compounding means more interest earned (or owed).

APR (Annual Percentage Rate) is the nominal rate. APY (Annual Percentage Yield) includes compounding and is the true yearly cost or return.

Start saving early and let compound interest work over time. Even small amounts grow significantly over 20–30 years in a high-yield savings account or investment account.