How to Calculate Interest in a Savings Account

October 21, 2026

Summary:
To estimate savings account interest, consider the principal, time, account activity, and either the stated interest rate and compounding assumptions or the disclosed Annual Percentage Yield (APY). Simple interest is calculated using the original principal, while compound interest includes interest previously added to the balance. Actual earnings may vary based on rates, deposits, withdrawals, fees, and the financial institution’s calculation and crediting methods.

Knowing how savings interest is calculated may help you compare account options and set savings goals. The result depends on the starting balance, interest rate or APY, time on deposit, compounding frequency, deposits, withdrawals, fees, and the financial institution’s calculation method.

Key highlights:

Savings account interest is influenced by principal, interest rate or APY, time, compounding, and account activity.
Simple interest is calculated only on the original principal, while compound interest includes interest previously added to the balance.
When the same stated annual interest rate and other assumptions are used, more frequent compounding generally produces a slightly higher estimated ending balance. APY reflects the interest rate and frequency of compounding.
Estimated earnings may change based on deposits, withdrawals, interest rates, compounding frequency, fees, and other account activity.

Understanding interest rate, principal, and time

These terms form the foundation of savings-interest calculations:

Principal: The starting balance used for an interest estimate. The balance may change as additional deposits, withdrawals, fees, and interest credits occur.
Interest rate: The percentage used to calculate interest before accounting for compounding.
APY: An annualized measure that reflects the interest rate and frequency of compounding.³
Time: The length of time funds remain on deposit.

Understanding these terms can make interest calculations easier to follow and may help you evaluate the assumptions used in an estimate.

What is the difference between simple and compound interest?

The main difference between simple and compound interest is how interest is calculated and whether previously earned interest is included in later calculations:

Simple interest: Interest calculated only on the original principal and not on previously earned interest.
Compound interest: Interest calculated on the principal and interest previously added to the balance. Under the same assumptions, this may result in more interest over time than simple interest.¹

Savings accounts may use compound interest, although calculation, compounding, and crediting methods vary by financial institution and account. Review the applicable account disclosures for details.
Learn more about compound interest.

Calculating simple interest step by step

The formula for a simple-interest estimate is:

Interest earned = Principal × Rate × Time

The interest rate is expressed as a decimal, and time is typically measured in years.

For example, suppose your principal is $1,000 and the account earns a hypothetical 3% annual simple interest rate for four years. First, convert the interest rate from 3% to 0.03. Then enter the values into the formula:

$120 = $1,000 × 0.03 × 4

That works out to $120 in estimated simple interest over four years.

Changing any of the formula inputs changes the estimated amount of interest earned.

Changing the principal while keeping the 3% rate and four-year period the same

Principal	Rate	Time	Estimated interest
$1,000	3%	4 years	$120
$2,000	3%	4 years	$240
3,000	3%	4 years	$360

Changing the rate while keeping the $1,000 principal and four-year period the same

Principal	Rate	Time	Estimated interest
$1,000	2%	4 years	$80
$1,000	3%	4 years	$120
$1,000	4%	4 years	$160

Changing the time period while keeping the $1,000 principal and 3% rate the same:

Principal	Rate	Time	Estimated interest
$1,000	3%	3 years	$90
$1,000	3%	4 years	$120
$1,000	3%	5 years	$150

These examples are for illustrative purposes only. Actual savings account earnings depend on the financial institution’s calculation method, compounding and crediting frequency, balance activity, fees, and other account terms.

Calculating compound interest step by step

Because compound interest is calculated on both the principal and interest previously added to the balance, the formula includes additional variables. The formula and variables below are based on FDIC educational guidance.²

A = P × (1 + r/n)^(n × t)

In this formula:

A is the estimated ending balance.
P is the principal.
r is the annual interest rate expressed as a decimal.
n is the number of compounding periods per year.
t is time in years.

Suppose the same $1,000 remains in a savings account for four years at a hypothetical 3% annual interest rate compounded annually. To estimate the ending balance:

Convert the rate to a decimal: r = 0.03
Enter the principal: P = 1,000
Select the compounding frequency: n = 1
Enter the time in years: t = 4

Using the compound-interest formula, the calculation looks like this:

$1,125.51 = $1,000 × (1 + 0.03/1)^(1 × 4)

The estimated ending balance is approximately $1,125.51, which represents approximately $125.51 in interest over four years.

This example assumes the interest rate remains unchanged and that there are no additional deposits, withdrawals, taxes, or fees. The example is for illustrative purposes only, may not reflect a financial institution’s actual calculation or crediting method, and does not represent a currently available product rate.

Understanding how the formula works may make it easier to evaluate savings accounts and compare how interest is calculated.

How compounding and account activity may affect estimated earnings

When the same stated annual interest rate and all other assumptions remain unchanged, more frequent compounding generally results in a slightly higher estimated ending balance. However, the difference between compounding schedules may be small, and compounding frequency should not be considered by itself when comparing savings accounts.

Interest calculation, compounding, and crediting practices vary by financial institution and account. Interest may be calculated daily and credited or added to the account balance on a different schedule. Review the applicable account disclosures for details.

APY may provide a useful annual comparison because it reflects the interest rate and frequency of compounding.³ Also consider fees, balance requirements, rate variability, access, and other account terms when comparing savings accounts.

Regular deposits may increase the balance used for subsequent interest calculations, while withdrawals may reduce it. Actual earnings may vary based on account activity, the applicable rate, fees, and the financial institution’s calculation and crediting methods.

Considerations that may support savings goals

Compare account terms: Review APYs, fees, balance requirements, access, eligibility, and other account terms.
Consider regular deposits: Additional deposits generally increase the balance used for subsequent interest calculations.
Understand the effect of withdrawals: Withdrawals reduce the balance available for future interest calculations.
Review applicable fees: Maintenance fees and other charges may reduce the account balance or earnings.
Revisit your savings approach: Savings goals and circumstances may change, so periodic review may be helpful.

Learn more about the Openbank High Yield Savings account

An Openbank High Yield Savings account may be an option to consider when comparing savings accounts. Review the current APY, fees, eligibility requirements, access options, and applicable disclosures to determine whether the account aligns with your needs.

Learn more about the Openbank High Yield Savings account or apply for an account online.

Savings-interest calculations: common questions, answered

When the stated interest rate and other assumptions remain the same, more frequent compounding generally produces a slightly higher estimated ending balance because previously earned interest may be added to the balance more often. The actual effect depends on the rate, balance, time, compounding and crediting methods, and other account terms.

Savings account interest rates may be variable and can change over time. Review the account's current rate, APY, and disclosures to understand how the rate is determined and whether it may change.

APY may provide a useful annual comparison because it reflects the interest rate and frequency of compounding.³ You may also estimate potential earnings using an assumed balance, time period, and applicable account terms.

Consider fees, balance requirements, access, eligibility, rate variability, and other terms when comparing accounts. Any calculation should be treated as an estimate rather than a guarantee of future earnings.

Actual interest may differ if the rate or balance changes, if deposits or withdrawals occur, if fees apply, or if the financial institution uses a different calculation or crediting method than the estimate assumes. Review the applicable account disclosures for additional information.

Sources:

¹ FDIC, Chapter 5: Compound Interest. Accessed October 14, 2026.
² FDIC, Money Smart for Young People, Grades 6–8 Educator Guide, “Understanding Compound Interest.” Accessed October 14, 2026.
³ Consumer Financial Protection Bureau, Appendix A to Part 1030: Annual Percentage Yield Calculation. Accessed October 14, 2026.

This content is for informational purposes only and does not constitute financial, legal, or investment advice. Please consult Openbank’s website or speak to a representative for the most up-to-date information.

Openbank is a division of Santander Bank, N.A. Member FDIC. Deposits at Santander Bank and its Openbank division are combined for FDIC insurance purposes and are not separately insured.