Statement APY Earned Calculator

Enter what one statement period actually paid — interest posted, average daily balance, days in the period, and any fees — and get back the annual percentage yield those figures work out to.

A bank quotes an APY. Weeks later a statement arrives carrying a dollar figure. The two are not comparable on sight, and that is the gap this calculator closes: it takes the interest posted for one statement period and solves backward for the annual percentage yield it represents.

Most savings calculators run forward — supply a rate, get a projected balance. This one runs backward, which is what you need when the question is whether an account paid what it said it would.

Four numbers from the statement, two from elsewhere

Interest posted this period. Regulation DD requires institutions that send periodic statements to disclose the interest earned for that period (12 CFR 1030.6(a)(2)). Use the amount credited for that cycle, not a year-to-date total.

Average daily balance. The input that causes trouble, because Reg DD does not require it — section 1030.6(a) mandates the APY earned, the interest, the fees and the length of the period, never the denominator behind them. Many statements print an average balance anyway; if yours does not, sum the end-of-day balances and divide by the day count. Do not substitute the closing balance: 12 CFR 1030.7 permits only the daily balance or average daily balance method and prohibits ending balance, low balance and investable balance methods.

Days in the statement period. Also required — the day count, or the beginning and ending dates (1030.6(a)(4)). Whether the cycle ran 28, 30 or 31 days changes how hard the period gets stretched to a year.

Fees charged this period. Required as well, itemized by type (1030.6(a)(3)). Enter maintenance and activity charges that reduced what you kept; zero is valid.

The last two inputs come from elsewhere. The APY you believe you are getting is the rate on the bank's disclosure page — optional, but supplying it turns the output into a comparison. The days-in-the-year selector, 365 or 366, only nudges the exponent; match what the institution states.

Why annualizing is not just multiplying by twelve

The calculator reduces the period to a plain ratio — interest divided by average daily balance — then scales it to a year with an exponent of days in the year over days in the period. A 31-day cycle in a 365-day year gives 11.774. Two lines come out of that exponent, and the difference between them is why APY exists separately from a nominal rate.

The simple annualized rate multiplies the period ratio by the exponent: if this pace repeated all year with nothing reinvested, what fraction of the balance would it add up to? It ignores compounding, so it always reads lower.

The APY earned line raises (1 + period ratio) to that exponent and subtracts 1 — the formula in 12 CFR Part 1030, Appendix A, Part II, the calculation the regulation assigns to the statement figure. It assumes credited interest stays put and earns alongside the principal, as a compounding account does.

The net of fees line runs the same compounded formula after subtracting fees from interest. It is not a regulatory figure — Reg DD computes APY earned on interest and discloses fees separately — but an account either left you ahead or it did not. If fees exceed interest the line goes negative; if they exceed the average balance itself, the formula has no real result and the calculator says so instead of printing a number.

Reading the three rate lines against each other

Suppose a statement shows $63.20 of interest over a 31-day period, the average daily balance was $19,000, a $5.00 maintenance fee was charged, and the advertised rate was 4.00% APY, on a 365-day year. Those figures are assumed for illustration, not market rates:

• Simple annualized rate: 3.92%
• APY earned: 3.99%
• APY earned net of the $5.00 fee: 3.67%
• Gap against the 4.00% expected: 33.3 basis points short
• What that gap is worth over a year on $19,000: $63.32

The story is in the spread. Gross APY earned landed 1.3 basis points under the advertised 4.00%, near enough that the rate itself was honored. The entire 33.3 basis point shortfall came from the $5.00 fee. That is a different problem with a different fix: the account is not underpaying, it is charging, and the remedy is a waiver or a different account. Our note on identifying and avoiding common fees covers where those charges hide.

The gap is measured against the net-of-fees figure rather than the gross, so it reflects what you kept. The dollar amount below it is that gap times the average daily balance — a sense of scale, not a forecast.

What a single period cannot settle

A statement is one snapshot, and several things bend the rate it implies without anything being wrong.

• A deposit or withdrawal mid-cycle can push the balance across a rate tier, leaving a blended APY that matches neither tier.
• A promotional rate that expired partway through does the same.
• Some accounts credit interest quarterly, so a statement showing none may reflect the crediting schedule, not the rate.
• APY earned looks backward at money already paid, while an advertised APY looks forward and can change at any time on a variable-rate account. A difference is not on its own a violation — see how changing rates affect money market returns.
• Interest posts rounded to the cent, and on a small balance that rounding alone moves the implied APY.
• Nothing here touches taxes. This measures what the bank paid, not what you keep.

One odd month is noise; a consistent shortfall across two or three statements is a finding.

Questions that come up when the numbers disagree

Why does APY earned read higher than the simple annualized rate?

Compounding. The simple line assumes interest sits idle; APY earned assumes it starts earning. They diverge more as the rate rises and as the period shortens relative to the year, since a shorter period means a larger exponent.

My statement prints its own APY earned and it does not match. Which is right?

Usually both. The discrepancy is normally in the denominator or day count: confirm you used the true average daily balance rather than a closing or average collected figure, and that the days match the cycle dates. If a material difference survives, put the question to the bank in writing.

The result says I came in short. Did the bank do something wrong?

Not necessarily. A shortfall against an advertised rate is a reason to ask, not evidence of a breach. Tiers, mid-cycle balance swings, a variable rate that moved, and fees all produce legitimate gaps. Work out which applies before deciding the account is mispriced rather than simply wrong for your balance.