CD Interest Calculator

About CD Interest Calculator

Compound interest is often called one of the most powerful forces in personal finance, because unlike simple interest, each period's earned interest gets added back into the balance and starts earning interest itself — growth compounds on top of growth. Understanding exactly how much a given rate and compounding schedule actually produces over time is essential for evaluating savings accounts, investments, and loans alike.

This tool calculates compound interest using the standard formula A = P(1 + r/n)^(nt), where P is the principal, r is the annual interest rate, n is how many times per year interest compounds, and t is the time in years. It supports the five most common compounding frequencies — annually, semi-annually, quarterly, monthly, and daily — since the same nominal annual rate produces a meaningfully different final balance depending on how often it compounds.

The difference compounding frequency makes is real, not just theoretical: a 5% annual rate compounded monthly grows faster than the same 5% compounded only once a year, because interest starts earning interest sooner and more often. This is why comparing two savings or investment offers with the same headline rate but different compounding schedules can matter more than it first appears.

This tool is genuinely useful for projecting how a savings account, CD, or investment will grow over a chosen time period, comparing offers with different rates or compounding frequencies, or working through finance coursework where compound interest is a foundational concept building toward more advanced topics like the time value of money.

How it works

1. Enter the principal amount. The starting balance or investment amount.
2. Enter the annual interest rate and compounding frequency. Choose how often interest compounds — annually through daily.
3. Enter the time period in years. See the final balance and total interest earned instantly.