Interest Calculator


Interest calculator for compound and simple interest. Calculate ending balance, regular contributions or withdrawals, interest rate, principal, or time period.

What Is an Interest Calculator?

An interest calculator (or interest rate calculator) projects how a starting balance grows with compound interest or simple interest, an optional recurring contribution, a rate, and a time period.

You can enter an initial investment, set recurring deposits, choose contribution timing, and switch between simple and compound interest. The calculator can also solve backwards, for the principal, contribution, rate, or time needed to reach a target ending balance, and shows the result as a chart and a yearly accumulation schedule.

Interest Growth Example

Start with $10,000, add $100 a month, and earn 5% compound interest for 10 years: the ending balance is about $31,998. Of that, $22,000 is your own money (initial investment plus contributions), and about $9,998 is interest earned.

Simple vs. Compound Interest

Simple interest is earned only on the principal, so it grows at a steady, predictable pace. Compound interest is also earned on interest already added to the balance, so it grows faster the longer it runs, and the compounding frequency (how often that interest gets added) makes a small but real difference to the final number.

Interest formulas

$$A = P \times \left(1 + \frac{r}{n}\right)^{n t}$$

Input
Interest type 
P
PMT
Contribution frequency
Payment timing 
t
r
%
Compounding frequency 
FV
Result
Ending balance
0.00

Using compound interest, the ending balance grows to 23288.95 over 10 years.

Interest typeCompound interest
Initial investment0.00
Total contributions0.00
Total principal0.00
Total interest payments0.00
Effective annual rate0.00%
Ending balance0.00
Fig. 1 · Interest breakdown

Interest Calculator FAQ

What is the difference between simple interest and compound interest?

Simple interest is calculated on principal only. Compound interest adds earned interest back to the balance, so future interest is earned on both principal and past interest.

Can this calculator include recurring contributions?

Yes. You can add recurring contributions and choose whether they happen annually, quarterly, or monthly. You can also choose whether they are added at the start or end of each contribution period.

Why does compounding frequency matter?

Compounding frequency affects how often interest is added to the balance in compound mode. More frequent compounding generally results in a slightly higher ending balance, all else being equal.

What does total principal mean here?

Total principal is the sum of your initial investment plus all recurring contributions. It excludes interest, so you can see how much of the ending balance comes from money you added yourself.

When should I use simple interest instead of compound interest?

Use simple interest for basic interest calculations where earnings do not themselves earn interest. Use compound interest for savings, investments, and accounts where interest is periodically added back to the balance.


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