How to Calculate CD Interest

The CD Interest Formula

To calculate CD interest, you need four inputs:

• Initial deposit
• Annual interest rate
• Term length
• Compounding frequency

The standard formula is:

A = P(1 + r/n)^(nt)

Where:

• P = principal or initial deposit
• r = annual interest rate
• n = number of compounding periods per year
• t = number of years
• A = final value at maturity

Your total CD interest is simply:

Interest earned = Final value − Initial deposit

Use the calculator below to estimate your CD earnings instantly.

Example: 1-Year CD Interest on $10,000

Suppose you deposit $10,000 into a 1-year CD at 5.00% APY-equivalent rate with monthly compounding.

The result will be close to:

• Initial deposit: $10,000
• Final value: about $10,511.62
• Total interest earned: about $511.62

If compounding were annual instead of monthly, the result would be slightly lower. That is why CD calculators often show both interest earned and APY.

APR vs APY in CDs

Many savers confuse APR and APY.

If two CDs advertise the same APR but one compounds daily and one compounds annually, the daily-compounding CD will have a slightly higher APY.

That is why APY is the better number for comparing CDs across banks.

How Compounding Frequency Changes CD Earnings

The more often interest compounds, the more frequently interest is added back to your balance. Then future interest is calculated on a slightly larger amount.

Example: $10,000 at 5% for 1 year

For most ordinary balances, the difference is not dramatic. But on larger deposits or longer terms, compounding frequency matters more.

Common CD Terms: 6-Month, 1-Year, 2-Year and 5-Year

CD rates often vary by term length:

• 6-month CDs are useful when you want a short lockup
• 1-year CDs are often a benchmark term for comparison
• 2-year CDs can offer a higher fixed rate if you do not need the money soon
• 5-year CDs lock your money much longer, so you need to compare carefully against other safe options

The right term depends on when you need the cash. A higher rate is not automatically better if it forces you into an early withdrawal later.

What Happens If You Withdraw Early?

Most CDs charge an early withdrawal penalty.

Typical penalties:

• 3 months of interest for shorter terms
• 6 months for 1-year CDs
• 9 to 12 months for longer CDs

That means you should not judge a CD only by the rate. Liquidity matters too. If you may need the money unexpectedly, compare with a high-yield savings account or read our CD vs savings account guide.

Are CD Earnings Taxable?

Yes. CD interest is generally taxable in the year it is credited, even if you leave the money in the account until maturity.

In the US, banks typically report interest on Form 1099-INT. So when estimating your real after-tax return, remember that your final take-home gain may be lower than the calculator's pre-tax total.

When a CD Calculator Is Most Useful

A CD calculator helps when you want to:

• Compare CD terms before opening an account
• Estimate how much a 1-year or 5-year CD will earn
• Compare monthly vs daily compounding
• Check whether a CD beats your current savings account
• Understand whether a small rate difference is actually meaningful

If you want market-based growth instead of guaranteed returns, compare your result with the investment calculator or compound interest calculator.

Key Takeaways

• CD interest depends on deposit amount, rate, term length, and compounding frequency
• APY is the best number for comparing different CDs
• A longer term or slightly higher rate does not always mean the best choice
• Early withdrawal penalties can reduce or erase part of the interest earned
• Use a CD calculator to compare options before locking up your money