How Do I Calculate Monthly Interest on My Savings Account

Calculating monthly interest on your savings account is essential for understanding your earnings and financial growth. This guide explains the process step-by-step, provides a calculator, and answers common questions.

How to Calculate Monthly Interest

Monthly interest is calculated by applying your savings account's annual percentage yield (APY) to the balance each month. Here's how to do it manually:

Find your account balance at the start of the month.
Determine the annual interest rate (APR or APY).
Convert the annual rate to a monthly rate by dividing by 12.
Multiply the monthly rate by your balance to get the monthly interest.
Add the interest to your balance to get the new balance.

For more accurate calculations, especially with compounding, use the formula below.

The Formula

Monthly Interest Formula

Monthly Interest = (Principal × Annual Interest Rate) ÷ 12

New Balance = Principal + Monthly Interest

The formula assumes simple interest calculation. For compound interest, the formula becomes more complex and depends on how often interest is compounded.

Worked Example

Let's calculate monthly interest for a $1,000 savings account with a 2.5% annual interest rate:

Principal = $1,000
Annual Interest Rate = 2.5% or 0.025
Monthly Interest Rate = 0.025 ÷ 12 ≈ 0.002083
Monthly Interest = $1,000 × 0.002083 ≈ $2.08
New Balance = $1,000 + $2.08 = $1,002.08

After one month, your balance would be $1,002.08.

Interest Compounding

Most savings accounts compound interest monthly. This means interest is calculated on the current balance, including previously earned interest. The formula for compound interest is:

Compound Interest Formula

New Balance = Principal × (1 + (Annual Interest Rate ÷ Compounding Periods per Year))^Number of Periods

For monthly compounding, the number of periods would be 1 for one month, 2 for two months, etc.

Note

Always check your account agreement to confirm the compounding frequency and whether the APY or APR is used.

FAQ

What is the difference between APR and APY?: APR (Annual Percentage Rate) is the simple annual interest rate. APY (Annual Percentage Yield) includes the effect of compounding, showing the actual return.
How often is interest calculated on savings accounts?: Most savings accounts calculate interest monthly, though some may compound daily or quarterly. Check your account terms.
Can I calculate interest manually?: Yes, using the formulas provided in this guide. For complex calculations, use our calculator for accuracy.
What if my interest rate changes?: If your interest rate changes during the month, you'll need to calculate interest using the rate that applies to each period.
How does interest affect my savings growth?: Interest compounds over time, meaning small amounts can grow significantly with consistent contributions and interest rates.