APY vs nominal rate: what's the difference?
The nominal interest rate is the number a lender or bank uses to calculate interest before accounting for how often that interest is applied. APY is the effective annual yield after compounding is factored in. They are the same only when interest is applied exactly once per year; for any more frequent compounding, APY is always higher.
This matters because compounding turns a nominal rate into a slightly bigger effective rate. A 5% nominal rate compounded monthly becomes a 5.1162% APY. Compounded daily it becomes 5.1267% APY. The more frequently interest is applied, the closer the APY approaches the continuous compounding limit — though the practical difference between daily and monthly is tiny.
Banks advertising savings accounts and CDs are required to quote APY, not the nominal rate, precisely so consumers can compare offers that may compound at different frequencies. When you see “4.75% APY” at one bank and “4.80% APY” at another, those numbers are directly comparable regardless of whether one compounds daily and the other monthly.
The compounding frequency table explained
The table in the calculator shows APY for five standard compounding schedules at your entered nominal rate. Annual compounding gives an APY exactly equal to the nominal rate — there is no intra-year interest to compound. Every more-frequent schedule adds a little more, because interest earned in earlier periods has time to earn its own interest before the year ends.
In practice, most savings accounts compound daily. Most CDs compound daily or monthly. Bonds pay semi-annual coupons (equivalent to semi-annual compounding). When a product quotes only the nominal rate, use the reverse mode in this calculator to find the APY at the institution's compounding frequency.
When to use APY → nominal reverse calculation
The reverse calculation is useful when you have the APY but need the nominal rate for a specific formula or spreadsheet. It is also useful when comparing loan products: if a lender quotes a monthly rate, you can find the nominal annual rate and then the APY to compare it against competing offers quoted differently.
Enter the APY and the compounding frequency the institution uses, and the calculator gives you the nominal rate. That nominal rate, divided by the compounding periods per year, gives the per-period rate your balance actually grows by each period.
If what you need is to see how a savings balance grows over time at a known APY, the savings goal calculator and the HYSA calculator do that calculation directly from an APY input.
Frequently asked questions
What is APY and how is it different from APR?
APY (Annual Percentage Yield) is the effective annual rate that accounts for compounding within the year. APR (Annual Percentage Rate) is the nominal rate stated without reflecting how often compounding occurs. A savings account with a 5% nominal rate compounded monthly has an APY of about 5.12% — the extra 0.12% is the effect of 12 compounding events per year instead of one. For savings accounts and CDs, banks are required to advertise APY so consumers can compare apples to apples.
How do I convert APR to APY?
The formula is APY = (1 + APR/n)^n − 1, where n is the number of compounding periods per year. For a 5% APR compounded monthly (n=12): APY = (1 + 0.05/12)^12 − 1 ≈ 5.1162%. Use the "Nominal → APY" mode above and select your compounding frequency to see the exact figure for any rate.
How do I convert APY back to a nominal rate?
The reverse formula is nominal rate = n × ((1 + APY)^(1/n) − 1). For a 5% APY with monthly compounding: nominal = 12 × ((1.05)^(1/12) − 1) ≈ 4.8889%. Use the "APY → Nominal" mode in the calculator above — enter the advertised APY and choose the compounding frequency, and you get the exact nominal rate.
Does it matter whether a savings account compounds daily or monthly?
The difference is real but small. At a 5% nominal rate, monthly compounding gives 5.1162% APY and daily gives 5.1267% APY — a gap of just 0.0105 percentage points. On a $10,000 balance over one year, that is about $1.05 in extra interest. Over longer horizons and larger balances the gap grows, but it remains the smallest of the three levers (rate, time, and contributions are far more impactful).
Why do banks advertise APY instead of the nominal rate?
Regulators require it for transparency. Without APY standardization, two banks could advertise "5% interest" while one compounds annually and another compounds daily — giving meaningfully different actual yields. APY converts any combination of nominal rate plus compounding frequency into a single comparable number, so consumers can directly compare offers from different institutions regardless of how their interest is applied.