Turn APY into dollars
For an unchanged balance held for a full year under those assumptions:
Interest = starting balance × APY expressed as a decimal.
The difference is $100 for the year. Whether that justifies moving the money depends on fees and how easily you can use the account. A higher percentage can be meaningful without being the only useful comparison.
For a shorter holding period, do not apply the full annual yield. Using a smooth effective-rate approximation, six months at 4% APY on $10,000 produces:
$10,000 × [(1.04)^(6/12) − 1] = $198.04.
Actual bank interest can differ because of daily balances, deposit dates, rounding, crediting rules, and rate changes. This is an educational estimate, not a bank statement calculation.
| Hypothetical APY | Starting balance | Interest after one year | Ending balance |
|---|---|---|---|
| 3% | $10,000 | $300 | $10,300 |
| 4% | $10,000 | $400 | $10,400 |
APY versus the stated interest rate
The stated interest rate and compounding frequency work together. Compounding means interest can itself begin earning interest. CFPB compound-interest explanation
For a constant nominal annual rate compounded at equal intervals:
APY = (1 + annual rate ÷ compounding periods per year)^(compounding periods per year) − 1.
A hypothetical 4% nominal annual rate compounded monthly becomes approximately 4.0742% APY. On $5,000 for a year, that produces about $203.71 of interest, under the same no-change assumptions.
If a bank has already given you an APY, its compounding effect is already included. Do not divide that APY by 12 and compound it again as though it were a nominal rate. For an equivalent monthly growth rate, use (1 + APY)^(1/12) − 1.
That distinction matters when using a calculator. Select the field or mode matching the number you actually have. The compound interest calculator helps you explore growth; read its rate assumptions before entering a bank's APY.
Why your interest may differ from the headline example
Account disclosures specify variable-rate, tiered-rate, fee, and other conditions. An APY comparison works best when you compare the same balance and holding period under each account's actual terms. CFPB sample deposit disclosures
Suppose an account's hypothetical $100 annual interest advantage comes with a $5 monthly fee you cannot avoid. Those fees total $60. Subtracting that cash cost leaves $40 of the initial advantage, before considering the effect of fee timing on interest. A zero-fee option could be easier to maintain even if its APY is lower.
| What changes? | Why the dollar result changes | What to check |
|---|---|---|
| You add money gradually | Later deposits have less time to earn interest | Deposit timing, not just your final balance |
| You withdraw money | The withdrawn amount stops contributing to future growth | The balance you expect to keep |
| The rate changes | One advertised APY no longer describes the entire year | Whether the rate is variable or fixed |
| Only part of the balance qualifies | The headline rate may not apply to every dollar | Tiers, caps, and qualification terms |
| Fees apply | Cash charges reduce what you retain | Monthly and transaction fees separately |
APY and APR answer different questions
APY is the deposit-yield measure discussed here. APR is used in borrowing disclosures. Do not compare the two labels without examining the product's calculation rules and costs. A savings APY alone does not establish whether keeping cash is preferable to paying down a particular debt.
Use the right next step
If you already know how much you want to save, use the savings goal calculator to estimate the monthly contribution. Run a zero-interest scenario as well as a positive-rate scenario to see how much the plan relies on interest.
If you are comparing accounts, write down four things before moving money: the APY that applies to your balance, recurring costs, how you will withdraw the money, and the identity of the bank holding it. The percentage becomes useful when those conditions are clear.
What does APY do for your savings comparison?
APY puts an account’s interest rate and compounding into a one-year comparison. It helps you compare offers on the same basis. It does not fix a variable rate for a year or tell you when a transfer will arrive. Check account access, fees, eligibility and deposit insurance alongside the percentage.
If an account held $5,000 for a full year at an unchanged 4% APY, the illustration would show $200 in interest before fees and tax. At 3% APY it would show $150. The $50 difference is useful context when deciding whether an account’s restrictions or transfer arrangements are worth accepting. These rates are examples, not current offers.
Use the Plandime calculator
A borrowing decision is easier to judge when you compare the monthly payment with the total cost.
Open calculator →Sources checked for this page
- CFPB, Regulation DD Appendix A · Primary source · Checked 2026-09-07
- CFPB, Compound interest · Primary source · Checked 2026-09-07