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Simple Interest
PopularCalculate simple interest on your investments.
I = P × r × tCompound Interest
PopularSee how your money grows with compounding.
A = P(1 + r/n)^(nt)Mortgage
Estimate monthly mortgage payments.
M = P[r(1+r)^n]/[(1+r)^n-1]Savings Account
Calculate savings growth with deposits.
FV = P(1+r)^n + PMT×...Loan Interest
Understand the total cost of your loan.
M = P[r(1+r)^n]/[(1+r)^n-1]CD Interest
Calculate Certificate of Deposit returns.
A = P(1 + r/n)^(nt)Interest Rate
Find the rate needed to reach your goals.
r = (A/P)^(1/t) - 1How It Works
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Your Complete Guide to Interest Calculators
What Is an Interest Calculator?
An interest calculator is a powerful financial tool that helps you compute how much interest you will earn on savings or pay on loans over a specific period. Whether you are planning for retirement, saving for a home, or comparing loan options, an online interest calculator gives you instant, accurate results without the need for complex manual calculations. Our free interest calculator supports multiple calculation types including simple interest, compound interest, mortgage payments, loan costs, CD returns, savings growth, and interest rate determination.
The best interest calculators account for variables like compounding frequency, regular contributions, and varying time horizons. With our suite of seven specialized calculators, you can model virtually any interest scenario and make confident financial decisions backed by math.
Simple Interest vs. Compound Interest
Understanding the difference between simple and compound interest is fundamental to making smart financial choices. Simple interest is calculated only on the principal amount using the formula I = P × r × t, where P is the principal, r is the annual interest rate, and t is the time in years. This means your earnings grow linearly — if you invest $10,000 at 5% simple interest for 10 years, you earn exactly $5,000.
Compound interest, on the other hand, is calculated on both the principal and the accumulated interest from previous periods. Using the formula A = P(1 + r/n)^(nt), where n is the number of times interest compounds per year, your money grows exponentially. The same $10,000 at 5% compounded monthly for 10 years yields $16,470.09 — earning $6,470.09 in interest instead of $5,000.
Mortgage Calculator: Plan Your Home Purchase
A mortgage calculator is one of the most important tools for anyone considering buying a home. Our mortgage interest calculator estimates your monthly payments based on the home price, down payment, interest rate, and loan term. Understanding your monthly obligation before committing to a mortgage helps you budget effectively and avoid financial stress.
The calculator also shows the total interest paid over the life of the loan, which can be eye-opening. For a $300,000 mortgage at 6.5% over 30 years, you would pay approximately $382,633 in interest alone — more than the original loan amount. By adjusting the interest rate or choosing a shorter loan term, you can see significant savings.
Savings Account Calculator: Grow Your Wealth
A savings account calculator helps you visualize how your money grows over time with regular deposits and compound interest. By entering your initial deposit, monthly contribution, annual interest rate, and time period, you can see exactly how much your savings will be worth in the future.
High-yield savings accounts currently offer annual percentage yields between 4% and 5%, making them attractive options for short to medium-term savings goals. Our savings interest calculator factors in monthly compounding to give you an accurate picture of your future balance.
Loan Interest Calculator: Know the True Cost
A loan interest calculator reveals the true cost of borrowing money. Whether you are considering a car loan, personal loan, student loan, or any other type of financing, understanding the total interest paid is crucial for making informed decisions. Our loan calculator shows your monthly payment amount, total interest paid, and overall repayment cost.
Even small differences in interest rates can translate to thousands of dollars over the life of a loan. By comparing different loan amounts, rates, and terms using our calculator, you can negotiate better deals and choose the most cost-effective financing option.
Interest Formulas
The math behind the calculators
Simple Interest
I = Interest · P = Principal · r = Rate · t = Time
Compound Interest
A = Amount · P = Principal · r = Rate · n = Compounds/yr · t = Time
Mortgage Payment
M = Monthly · P = Principal · r = Rate · n = Payments
Future Value + Deposits
FV = Future · P = Initial · PMT = Deposit · r = Rate · n = Periods
Common Questions
What is compound interest and how does it work?
Compound interest is interest calculated on the initial principal and also on the accumulated interest from previous periods. Unlike simple interest, which is only calculated on the principal, compound interest grows exponentially over time. The more frequently interest is compounded (monthly, daily, etc.), the faster your money grows.
How do I use the interest calculator?
Select the type of calculator you need, enter your values using the sliders or number inputs, and see your results instantly. All calculations update in real-time as you adjust your values, so you can quickly compare different scenarios.
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal using I = P × r × t. Compound interest is calculated on both the principal and accumulated interest using A = P(1 + r/n)^(nt). For example, $10,000 at 5% for 10 years yields $5,000 in simple interest but $6,288.95 compounded monthly.
How much interest will I pay on a mortgage?
The amount of interest you pay on a mortgage depends on your loan amount, interest rate, and loan term. For a $300,000 mortgage at 6.5% over 30 years, you would pay approximately $382,633 in interest over the life of the loan. Use our calculator to see how different rates and terms affect your total cost.
Are these financial calculators free to use?
Yes, all our financial calculators are completely free with no sign-up required. You get instant access to all seven calculators with accurate results using standard financial formulas.
How much interest will I earn on a savings account?
The interest earned on a savings account depends on your initial deposit, monthly contributions, interest rate, and time period. Saving $500 monthly at 4% annual interest for 10 years would earn approximately $14,641 in interest, turning your total deposits of $60,000 into $74,641.
What is the best interest rate for a CD?
CD interest rates vary based on the term length and financial institution. Generally, longer CD terms offer higher rates. Our CD calculator helps you compare different rates and terms to find the best return on your investment.
How is car loan interest calculated?
Car loan interest is typically calculated using the amortization formula, where you pay a fixed monthly amount that includes both principal and interest. Our loan calculator helps you understand the total cost of your car loan including all interest charges.
Can I use these calculators on my phone?
Absolutely! All our calculators are fully responsive and work perfectly on smartphones, tablets, and desktop computers. The slider controls and number inputs are optimized for touch screens.
How accurate are the calculator results?
Our calculators use standard financial formulas accepted in the banking and finance industry. Actual outcomes may vary due to factors like fees, taxes, and inflation, but the mathematical calculations are highly accurate.