Interest Calculator
Use our interest calculator to see how your money can grow over time with simple or compound interest. Calculate future values, interest earnings, and compare different interest rates and compounding frequencies.
Interest Calculator
How Interest Works
Interest is the cost of borrowing money or the reward for saving it. It's calculated as a percentage of the principal amount (the initial amount of money) over a specific period of time.
When you save or invest money, you earn interest on your capital. When you borrow money, you pay interest on the loan. Interest can be calculated in two main ways: simple interest and compound interest.
Types of Interest
Simple Interest
Simple interest is calculated only on the initial principal. No matter how long the term is, interest is not earned on previously accumulated interest. Simple interest is typically used for short-term loans or bonds.
Compound Interest
Compound interest is calculated on the initial principal and also on the accumulated interest over previous periods. This means your money grows exponentially over time, making it powerful for long-term investments.
Compounding Frequency
The frequency with which interest is calculated and added to the principal affects the total amount earned. Common compounding periods include daily, monthly, quarterly, semi-annually, and annually. More frequent compounding results in higher returns.
Interest Calculation Formulas
Simple Interest Formula
Simple interest is calculated using the formula:
$$A = P(1 + rt)$$
Compound Interest Formula
Compound interest is calculated using the formula:
$$A = P(1 + r/n)^{(nt)}$$
How to Use Our Interest Calculator
- Enter the principal amount (initial investment or loan amount).
- Input the interest rate as an annual percentage.
- Specify the time period in years, months, or days.
- Select the interest type (simple or compound) and, if applicable, the compounding frequency.
The calculator will instantly show you the total amount, interest earned, and effective annual rate. You can also view a detailed breakdown of how your money grows over time through charts and tables.
Interest Calculation Examples
Short-Term Savings With Simple Interest
A saver deposits $5,000 at 4% simple interest for 3 years and wants to estimate the ending balance.
Inputs: Principal = $5,000, rate = 4%, time = 3 years, interest type = simple.
What the result shows: The calculator shows how much interest is earned without interest-on-interest, making the growth easy to compare with a basic savings product or note.
This is helpful when evaluating products that quote a flat annual return and do not compound frequently.
Longer Investment Horizon With Monthly Compounding
An investor wants to project how $10,000 could grow over 10 years at 6% compounded monthly.
Inputs: Principal = $10,000, rate = 6%, time = 10 years, interest type = compound, compounding = monthly.
What the result shows: The calculator reveals the higher ending balance and effective annual rate created by monthly compounding.
This makes it easier to compare bank products, CDs, or investment assumptions that share a similar nominal rate but compound at different intervals.
Interest Calculator FAQs
When should I use simple interest instead of compound interest?
Use simple interest when interest is calculated only on the original principal, such as some short-term loans or basic note agreements. Use compound interest when earned interest is added back to the balance and continues generating returns over time.
Why does compounding frequency change the final amount?
More frequent compounding adds interest to the balance sooner, so later periods earn interest on a larger amount. Even if the stated annual rate stays the same, monthly or daily compounding usually produces a slightly higher ending balance than annual compounding.
What does the effective annual rate mean?
The effective annual rate converts a nominal rate and compounding schedule into a true one-year growth rate. It gives you a cleaner apples-to-apples comparison between products that use different compounding frequencies.
Can I use this interest calculator for loans as well as savings?
Yes. The same formulas can estimate growth on savings or the interest cost on a loan balance. The main difference is how you interpret the result: savers focus on earnings, while borrowers focus on financing cost.