APR ↔ APY Converter (Effective Yield & Periodic Rate)

1. One aligned box for all the key numbers

The converter is built to mirror your internal sheets: a single, compact summary that tells you, “What’s the real annual yield for this quoted rate?” without jumping between fields or scanning a big table. You choose a compounding frequency, enter either APR or APY once, and the tool returns the matching rate, the per-period rate, and concrete dollar examples.

2. Start with the compounding that matches your product

Always align the frequency with reality. Savings and many loan products compound monthly, some high-yield accounts compound daily, and certain bonds or CDs compound annually or semiannually. By locking the compounding first, the APR↔APY math is tied to how interest is actually applied, which keeps comparisons honest.

3. Enter exactly one input: APR or APY

If you’re reading a marketing sheet or a loan offer, you usually see APR. Enter that APR and your frequency to get the effective APY. If you’re reverse-engineering a product that only publishes APY, enter APY instead to see the underlying nominal APR. Entering both at once creates conflicting constraints, so the tool prevents it and prompts you to choose one.

4. Understand the formulas (without overcomplicating it)

For m compounding periods per year, an APR of R% turns into an APY of (1 + R/m)^m − 1. Going backwards, an APY of Y% corresponds to an APR of m × ((1 + Y)^1/m − 1). When you select “Continuous”, the model switches to the textbook limit: APY = e^R − 1 and APR = ln(1 + Y). The calculator applies the right branch automatically so your summary is always internally consistent.

5. Use the periodic rate for projections and checks

The periodic rate is the nominal rate per month, week, or day (depending on your selection) that compounds up to the displayed APY. This is the number you can plug directly into quick projections: multiply the current balance by the periodic rate to estimate next period’s interest (ignoring day-count quirks). It’s also a good way to sanity-check whether a quoted APY aligns with how often interest is applied.

6. Anchor decisions on the 1-year USD impact

To keep everything tangible, the summary includes 1-year examples on $1,000 and $10,000 in USD at the computed APY. That mirrors how most teams think about customer value and funding costs: “If we promise this yield, what’s the dollar impact on typical balances?” You can scale the same yield to your real exposure in your own models.

7. Remember what’s not included

The tool assumes a constant rate, no extra fees, and a clean year of compounding. In practice, banks use specific day-count conventions, promotional periods, and fee structures, and those can move the realized yield or cost away from the theoretical APY. Treat these outputs as your standardized baseline, then adjust externally for fees and behavior.

8. Use it as a shared reference, not a black box

Because the logic is transparent and matches standard finance formulas, product, growth, and finance teams can rely on the same aligned summary. That makes it easier to QA rate sheets, compare offers across institutions, and document why a published APY makes sense for a given APR and compounding schedule.