APR Calculator for Savings Accounts

This savings account APR calculator estimates how much interest a deposit could earn over a year at a stated annual percentage rate, before taxes or account fees. Enter your starting balance and annual rate to see estimated interest and the ending balance, assuming the rate stays fixed and interest is compounded monthly.

Formula

The calculator applies monthly compounding for 12 months. It converts the annual percentage rate (APR) into a monthly rate, raises the monthly growth factor to the 12th power, and applies that growth to the starting balance.

• Starting balance (bal): the amount deposited at the beginning, in dollars.
• Savings APR (apr): the annual rate entered as a percentage, such as 4 for 4% per year.
• Monthly rate: apr ÷ 1,200, expressed as a decimal.
• Interest earned: bal × [(1 + apr ÷ 1,200)¹² − 1], in dollars.
• Ending balance: bal × (1 + apr ÷ 1,200)¹², in dollars.

This is a one-year estimate with no additional deposits or withdrawals. The APR is treated as a nominal annual rate divided into monthly periods; the calculation does not assume daily compounding or a changing rate.

Worked Example

Using the default inputs: a $10,000 starting balance and 4% APR. First convert the APR to a monthly rate: 4 ÷ 1,200 = 0.0033333333, or about 0.3333% per month.

1. Monthly growth factor: 1 + 0.0033333333 = 1.0033333333.
2. Growth over 12 months: (1.0033333333)¹² ≈ 1.040741542.
3. Ending balance: $10,000 × 1.040741542 = $10,407.41542, which rounds to $10,407.42.
4. Interest earned: $10,407.41542 − $10,000 = $407.41542, which rounds to $407.42.

The displayed outputs are therefore $407.42 in estimated interest and a $10,407.42 ending balance. The interest output is calculated from the unrounded growth factor and rounded to cents; the ending balance is calculated separately and also rounded to cents.

Assumptions

• The entered APR stays fixed for the full year.
• The starting balance is in the account for the entire year; there are no extra deposits or withdrawals.
• Interest compounds monthly, using the APR divided by 12.
• Fees, taxes, minimum-balance conditions, promotional-rate expiry, and account-specific calculation conventions are not included.

APR and APY: What Is the Difference?

APR is an annualized rate that generally does not express the full effect of compounding in the same way as annual percentage yield (APY). APY reflects how often interest is compounded over a year, so it is useful when comparing the annual growth implied by different compounding schedules. For a savings account, the advertised rate may be presented as APY rather than APR. Check the account’s official rate disclosure and use the corresponding rate and compounding method rather than treating APR and APY as interchangeable.

For example, at 4% APR compounded monthly, the effective one-year increase in this calculator is about 4.0742%, before fees or other account activity. A stated 4% APY, by contrast, represents a 4% annual yield under the terms used to calculate that APY; it should not automatically be entered as a 4% APR in a monthly-compounding formula. Small differences in rate wording and compounding can change the result.

How to Use and Interpret the Estimate

Enter the opening balance and the annual rate shown in the account information. Enter a percentage as a whole percentage number: use 4 for 4%, not 0.04. The result estimates interest for one year under the assumptions above. It is not a promise of what an account will pay.

The estimate is most directly useful for a balance that remains unchanged except for interest. If you add money during the year, the deposits earn interest only after they arrive, so applying the full-year formula to the final total would overstate earnings. Withdrawals, rate changes, tiered rates, and balance thresholds also make actual interest differ. For a more precise estimate with regular contributions, each deposit needs to be modelled from its deposit date or over the account’s actual interest-calculation periods.

Common Calculation Mistakes and Limits

• Confusing APR with APY: confirm which annual rate the account disclosure provides and how it is defined.
• Entering a decimal instead of a percent: enter 4 for 4%, not 0.04.
• Assuming the rate cannot change: a variable account rate may change during the year, making a fixed-rate estimate inaccurate.
• Ignoring cash flows: deposits and withdrawals change the balance and the time each dollar earns interest.
• Rounding too early: intermediate calculations retain precision, while displayed dollar amounts are rounded to cents. Actual institutions may use their own stated daily-balance and rounding procedures.

This calculator is for an illustrative one-year calculation, not a forecast of future earnings or a comparison of specific accounts. To understand an actual account’s yield, compounding method, rate conditions, and charges, refer to its current disclosure. The result is an estimate; the account disclosure gives the applicable figures and terms.

Frequently Asked Questions

How much interest will $10,000 earn in a savings account at 4% APR?
With monthly compounding and an unchanged balance and rate for one year, the estimate is $407.42 in interest, producing a $10,407.42 ending balance before fees or taxes.

Should I enter APR or APY for a savings account?
Use the rate that matches the calculator’s stated method. This calculator takes APR and assumes monthly compounding. If the account gives an APY, do not assume it is the same as APR; use the account’s disclosed yield and calculation details for a like-for-like estimate.

Does this calculator include monthly deposits?
No. It assumes one starting deposit and no later transactions. Regular deposits need a calculation that accounts for when each contribution is made and how long it earns interest.

Why might my actual interest differ?
The account’s rate may change, the balance may vary, and the provider may calculate interest using daily balances or other disclosed terms. Fees and account conditions can also affect the amount credited.

Is savings account interest guaranteed for a full year?
This estimate assumes a fixed rate for the year, but the actual rate terms depend on the account. Check its current disclosure for whether and when the rate can change.

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in bal | Starting balance | $ | 10000 | 0 | 100000000
in apr | Savings APR | % | 4 | 0.01 | 100
out int | Interest earned in one year | $ | bal * ((1 + apr / 1200) ^ 12 - 1) | 2
out end | Ending balance | $ | bal * (1 + apr / 1200) ^ 12 | 2