Free Tool · No Account Required

See exactly what
your money earns
over time.

Simple, compound, continuous, or monthly accrual — with a full year-by-year breakdown and growth chart. Know your number before you commit.

Used by savers, investors, and anyone doing the math first. Always free.

Interest Calculator

Simple · Compound · Continuous · Monthly Accrual

Configure Your Calculation

$
% / yr
% / mo
e.g. 1.5%/mo · Tax liens, penalties, some credit products
Enter number of years
$
Added each month on top of principal
Final Balance
Total Interest Earned
Effective APY

Growth Over Time

Breakdown by Year

PeriodBalanceInterest This PeriodTotal ContributedCumulative Interest

The math isn't complicated. It's just never laid out clearly.

Most interest calculators give you one number and call it done. But the number that matters isn't just your final balance — it's how you got there. What's the actual split between principal, contributions, and interest? What does compounding daily versus annually actually cost you? What does 1.5% per month look like on a tax lien over three years? This tool shows you the math, the period-by-period growth, and the formula behind every result — so you can make an informed decision, not just accept a headline rate.


Built for anyone doing the math before they commit.

Interest calculations come up constantly — savings accounts, loans, investments, tax liens, business decisions. Here's who checks their numbers here.

🏦

Savers & Depositors

Compare what different savings account rates actually mean over five or ten years — not just the APY headline, but the real dollar difference.

📈

Investors

Model long-term compound growth with regular monthly contributions. See what consistent investing actually does to the curve over decades.

🏠

Tax Lien Investors

Calculate exact accrual on tax lien certificates using the monthly rate method. Know your redemption value at any point in the lien period.

👩‍💼

Small Business Owners

Evaluate financing options, calculate interest on business lines of credit, or model returns on capital you're considering deploying.

🎓

Students & Educators

Visualize the difference between simple and compound interest for personal finance education. The period-by-period table makes the concept concrete.

📋

Financial Planners

Quick client-facing projections without spinning up a spreadsheet. Run three scenarios in three minutes and share the numbers on the spot.


Good questions. Simple answers.


What's the difference between the four methods?

Simple interest is calculated only on the original principal — it doesn't grow on itself. Compound interest calculates on both principal and accumulated interest at a set frequency (daily, monthly, annually, etc.). Continuous compounding is the theoretical limit using the mathematical constant e. Monthly Rate accrual applies a fixed percentage each month to the running balance — this is how most tax liens, some credit products, and certain penalties are structured.

When should I use Monthly Rate instead of Compound?

Use Monthly Rate when the interest rate is stated as a percentage per month rather than per year. Tax lien certificates in most states are issued with a monthly statutory rate (e.g. 1.5%/month in many jurisdictions). Some credit cards and penalty structures also work this way. The tool converts the monthly rate to an annualized equivalent so you can compare it to other products.

What is APY and how is it different from the stated rate?

APY (Annual Percentage Yield) is the effective annual return when compounding is factored in. A 5% rate compounded monthly produces an APY of about 5.116% — because interest earned early in the year earns interest itself in later months. For monthly rate accrual, the tool shows both the simple annualized rate (monthly × 12) and the true compounded APY so you can compare apples to apples.

Can I calculate interest for a period shorter than one year?

Yes — use the months toggle on the time period input. The tool calculates correctly for any number of months and shows a month-by-month breakdown in the table.

Can I embed this calculator in my platform or client portal?

Yes — we build custom versions for financial platforms, credit unions, tax lien investment platforms, HR benefits portals, and financial education programs. A branded embed with your rates pre-populated, your color scheme, and your compliance language is a one-week build. Talk to us about a custom build →

Want this built for your platform?

Custom-branded interest calculators for credit unions, financial platforms, tax lien investment tools, HR benefits portals, and educational programs — with your rates, your branding, and your compliance language built in.

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