Calculate Monthly Interest on Savings Account

Calculating monthly interest on a savings account helps you understand how your money grows over time. This calculator provides an easy way to estimate your monthly interest earnings based on your principal amount, annual interest rate, and the number of months you'll keep the money in the account.

How to Calculate Monthly Interest

Monthly interest is calculated by taking the principal amount, multiplying it by the monthly interest rate, and then multiplying by the number of months. The monthly interest rate is derived from the annual percentage rate (APR) by dividing it by 12.

Key Terms

Principal (P): The initial amount of money deposited into the savings account.
Annual Percentage Rate (APR): The yearly interest rate charged by the bank.
Monthly Interest Rate: The APR divided by 12.
Number of Months (n): The duration the money will remain in the account.

For example, if you deposit $1,000 at an APR of 5% for 12 months, your monthly interest rate would be 0.4167% (5% ÷ 12). The monthly interest would then be $1,000 × 0.004167 × 12 = $4.80.

The Formula

The formula for calculating monthly interest is straightforward:

Monthly Interest Formula

Monthly Interest = Principal × (Annual Interest Rate ÷ 12) × Number of Months

Or in mathematical notation:

I = P × (r ÷ 12) × n

Where:

I = Monthly Interest
P = Principal amount
r = Annual interest rate (in decimal)
n = Number of months

This formula assumes simple interest, where the interest is calculated only on the original principal. For compound interest, which is more common in savings accounts, the calculation is more complex and involves the use of the compound interest formula.

Worked Example

Let's work through an example to illustrate how to calculate monthly interest.

Example Calculation

Suppose you deposit $5,000 into a savings account with an annual interest rate of 3%. You want to know how much interest you'll earn each month if you leave the money in the account for 6 months.

Convert the annual interest rate to a monthly rate: 3% ÷ 12 = 0.25% or 0.0025 in decimal.
Multiply the principal by the monthly rate: $5,000 × 0.0025 = $12.50.
Multiply by the number of months: $12.50 × 6 = $75.00.

Therefore, you would earn $75.00 in monthly interest over the 6-month period.

Note

This example uses simple interest. In reality, many savings accounts use compound interest, which means the interest is calculated on both the initial principal and the accumulated interest from previous periods.

How Compounding Works

Compounding is the process where interest is calculated on the initial principal and also on the accumulated interest of previous periods. This can significantly increase the amount of interest earned over time.

The formula for compound interest is:

Compound Interest Formula

A = P × (1 + r/n)^(n×t)

Where:

A = the amount of money accumulated after n years, including interest.
P = the principal amount (the initial amount of money)
r = the annual interest rate (decimal)
n = the number of times that interest is compounded per year
t = the time the money is invested for, in years

For monthly compounding, n would be 12. The monthly interest can then be calculated by taking the difference between the amount after one month and the principal.

FAQ

What is the difference between simple interest and compound interest?: Simple interest is calculated only on the original principal amount, while compound interest is calculated on the initial principal and also on the accumulated interest of previous periods. Compound interest typically results in higher earnings over time.
How often is interest calculated in a savings account?: Most savings accounts calculate interest monthly, meaning the interest is added to your account once per month. Some accounts may offer daily or annual compounding, which can affect your earnings.
Can I withdraw money from a savings account without penalty?: This depends on the specific terms of your savings account. Some accounts allow unlimited withdrawals without penalty, while others may have restrictions or fees for early withdrawals.
What factors can affect the interest rate on my savings account?: Factors that can affect your interest rate include the type of account, the bank's policies, your account balance, and market conditions. Some banks offer higher rates for larger deposits or for customers who meet certain criteria.
Is it better to leave money in a savings account or invest it?: The decision depends on your financial goals and risk tolerance. Savings accounts typically offer lower returns but are very safe. Investments, such as stocks or bonds, can offer higher returns but come with more risk.