How to Calculate Savings Account Interest From a Daily Balance

A savings account balance rarely stays still for an entire month. You deposit a paycheck, pay a bill, or transfer money out. If you want to estimate the interest on your statement, multiplying the closing balance by the advertised annual rate will usually give the wrong answer. The dates and balances matter.

The practical method is to divide the statement period into stretches with the same balance, calculate interest for each stretch, then add the results. First, check what the bank actually discloses about balance calculation, compounding, and when interest is credited. The example below shows the arithmetic, not a promise that every bank will produce the same statement total.

Start with the rate and the bank's calculation method

Find the interest rate in the account disclosure. It is not necessarily the same number as the annual percentage yield, or APY. APY includes the effect of compounding under the advertised assumptions. If you put APY straight into a daily-rate formula, you may count some compounding twice. For the distinction, see our APY versus interest rate guide.

Next, check whether the bank uses a daily balance or average daily balance method and when deposits begin earning interest. US consumer deposit account disclosures must explain the balance method and other relevant terms. The Consumer Financial Protection Bureau's Regulation DD disclosure rule describes those requirements. Account terms, not a general online example, control your actual payment.

For a straightforward daily-balance estimate, use this formula for each period in which the balance and rate remain unchanged:

Interest for the period = balance × annual interest rate × number of days ÷ days in the rate year.

Write the annual rate as a decimal: 5% becomes 0.05. The denominator is commonly 365, though a bank may use 366 for a leap year where permitted. The CFPB's interest payment rule explains daily-balance and average-daily-balance methods, including the daily-rate convention. Check your bank's agreement rather than assuming its exact convention.

A worked example with a mid-month deposit

Suppose this is a hypothetical 30-day statement period. Your balance is $1,000 for the first 15 days. A $1,000 deposit then clears, bringing the balance to $2,000 for the next 15 days. The annual interest rate stays at 5%, and for this illustration we use 365 days in the rate year. We also assume interest is credited only after the statement period, so credited interest does not change the balance during these 30 days.

Days 1 through 15: $1,000 × 0.05 × 15 ÷ 365 = about $2.0548.
Days 16 through 30: $2,000 × 0.05 × 15 ÷ 365 = about $4.1096.
Total estimated interest: $2.0548 + $4.1096 = about $6.1644, or $6.16 when rounded at the end.

Using the $2,000 closing balance for all 30 days would overstate this example. Using the $1,000 opening balance throughout would understate it. That is why the date of a transaction matters, not just its amount. If you make several deposits or withdrawals, create another row each time the interest-earning balance changes.

You can also summarize this exact example with a weighted average balance. The balance was $1,000 for half the period and $2,000 for half, so its 30-day average is $1,500. Then $1,500 × 0.05 × 30 ÷ 365 gives the same unrounded $6.1644. This is a useful cross-check, but your bank's disclosed average-daily-balance method, eligibility rules, and crediting schedule still determine the actual statement.

How to set up your own calculation

Open a spreadsheet or make a small table with four columns: start date, ending date, balance, and number of days. Record the balance that actually earns interest after each transaction. If the rate changes during the month, start a new row on the effective date even if your balance does not change. Multiply each row's balance by its applicable annual rate and the row's day count, divide by the stated day-count basis, and sum the unrounded row results.

Be careful with date boundaries. If your deposit starts earning interest on Tuesday, do not include Monday in the higher-balance row. Conversely, do not omit a day at the end of the statement period. A quick check is that your row day counts add up to the number of days on the statement. Keep more than two decimal places until the final total because rounding each row separately can create a small discrepancy.

If you are trying to reconcile a real statement, use the bank's transaction posting dates, not only the dates you initiated transfers. Also check whether a deposit had a hold, whether a promotional rate expired, and whether the account had separate balance tiers. These are questions to verify in your account terms or with your bank, not assumptions to insert into the formula.

Why the statement may differ from your estimate

Compounding and crediting are different events. Interest can be calculated or accrued daily while the bank credits it monthly. If credited interest becomes part of the earning balance during a period, later interest may include interest on interest. The simple worked example intentionally excludes that because it assumes a single credit at the end. To estimate longer-term growth with a known rate and frequency, use the ToolNimbly compound interest calculator.

APY is not a promise of one month's payout. APY is an annualized comparison measure calculated under stated assumptions. Your deposits, withdrawals, rate changes, and the statement period affect the actual dollars earned. The CFPB's APY rule sets out the disclosure calculation, including assumptions that may not match your account activity.

Rates and rounding can change the last cents. A bank might round daily accruals or round only at crediting, and a leap-year convention can change the denominator. Some accounts also use tiers or minimum balances. If your estimate differs by more than a trivial amount, compare the exact rate, posting dates, balance method, and accrual details on the statement or disclosure. Do not assume your account is wrong just because it differs from a simplified online calculation.

Daily interest versus daily compounding

The phrase “calculated daily” does not, by itself, tell you how often interest is added to the balance. Daily accrual describes how often the bank measures earned interest. Compounding describes when earned interest itself starts earning more interest. A bank could accrue each day and credit interest monthly. Read both the compounding and crediting fields in the disclosure before projecting a year's earnings.

This distinction also explains why two accounts showing the same annual interest rate can advertise different APYs. More frequent compounding can increase the annual result when all else is equal. If your question is about that comparison specifically, our daily versus monthly compounding guide walks through it. The present calculation focuses on changing balances inside one statement period.

A final checklist before trusting the number

Use the account's annual interest rate, not APY, for the illustrated daily-rate method.
Split the period whenever the earning balance or rate changes.
Use actual posting and accrual dates, then verify that the day counts cover the whole period.
Match the disclosed day-count basis, balance method, and crediting schedule.
Round at the end for an estimate and expect possible differences from the bank's own rounding rules.

The goal is a defensible estimate that you can explain, not a universal formula that overrides your account agreement. Once you have the dates, balances, and rate, the arithmetic is simple. The important work is identifying which dollars earned interest on which days.