Calculator Methodology
This page explains the math behind every calculator on this site.
HYSA calculator formula
The HYSA calculator uses monthly compounding with an additional regular contribution each month:
Convert the APY into its equivalent monthly rate:
monthly_rate = (1 + APY) ^ (1/12) − 1
Then for each month m:
balance = balance * (1 + monthly_rate)
balance = balance + monthly_contribution
APY is the annual percentage yield, which means it already includes the effect of compounding. So it cannot simply be divided by twelve: doing that treats it as a nominal rate and overstates the result. The monthly rate above is the one that, compounded twelve times, reproduces exactly the APY you entered. Contributions are added at the end of each month, after that month’s interest. This page previously documented interest_m = balance * (APY / 12) and claimed it approximated daily compounding. It did not. It returned $10,459.40 on $10,000 at 4.50% APY over one year, where the definition of APY makes the answer exactly $10,450.00. The formula and every calculator using it were corrected on 30 August 2026.
Compound interest formula
- A = final amount
- P = principal
- r = annual rate (decimal)
- n = compounding periods per year
- t = years
APY vs APR
APY (Annual Percentage Yield) includes the effect of compounding. APR (Annual Percentage Rate) does not. All inputs on this site use APY, which is what banks advertise for savings accounts.
APY = (1 + APR/n)^n - 1, where n is the number of compounding periods per year. For a 5.00% APR compounded daily, the APY is 5.127%.
Compounding assumption
Every calculator that asks for an APY converts it to an equivalent monthly rate and adds the contribution at the end of each month. Because the conversion is exact, the twelve monthly steps reproduce the APY you entered, whatever frequency your bank actually compounds at internally. A bank may calculate interest daily, compound it daily and credit it monthly. An APY is designed to express the resulting effective annual yield, which is why it is the figure to compare accounts on and the figure these calculators take. The CD calculator is the one exception worth naming: it asks for the advertised APY and does not ask for a compounding frequency, because applying one to an APY would compound the yield twice. Converting a nominal rate into an APY is a separate job and has its own tool.
The CD calculator assumes the deposit stays in for the full term with no early withdrawal. Real CDs charge a penalty if you pull out early (usually 3 to 12 months of interest).
Tax treatment
Calculators on this site show gross interest earned. They do not subtract taxes. Interest from a HYSA or CD counts as ordinary income on your federal tax return. Most taxpayers owe 12% to 24% on this income.
State tax rules vary. Some states (Florida, Texas, Nevada, and others) do not tax interest. Some (California, New York) tax it at the state income tax rate.
The bank sends a 1099-INT each January if you earned $10 or more in interest. Source: IRS Publication 550: Investment Income and Expenses.
FDIC insurance
All accounts ranked on the Best HYSAs page are FDIC insured up to $250,000 per depositor, per insured bank, per ownership category. Joint accounts get up to $500,000.
FDIC insurance is backed by the U.S. government. No depositor has lost FDIC-insured funds since the FDIC began in 1933. Source: FDIC Deposit Insurance Overview.
Rate data sources
We do not publish any bank’s APY. This is deliberate, and it is worth explaining because most comparison sites do the opposite.
Savings rates are variable. A bank can change one overnight and usually does so without announcing it. A figure typed onto a web page is correct on the day it is typed and slowly stops being true afterwards, with nothing on the page to signal that it has. We used to publish a table of rates here. When we re-checked it in August 2026 every figure was between 80 and 135 basis points above what the banks were actually paying, and the page gave a reader no way to know.
We also could not fix it reliably. Several banks block automated requests to their rate pages, others render the number in the browser where a simple fetch cannot read it, and the third-party sites that do republish rates disagree with each other about the same account on the same day. Without a maintained, licensed rate feed there is no way to keep a per-bank number honest between updates, and a confidently wrong number on a savings page is worse than no number.
So we publish what we can stand behind. National averages come from FDIC National Rates and Rate Caps, published monthly. Federal funds data comes from the Federal Reserve. For everything else we compare the parts of an account that do not move week to week: minimum balance, monthly fees, ATM access, whether the rate is tiered, FDIC cover, and whether the account is still open to new customers. Each account links to the bank’s own rate page, which is the only place a current rate is authoritative.
Any percentage you see in an example on this site is illustrating the arithmetic, not quoting an offer. The calculator uses whatever rate you type into it.
We do not guarantee current accuracy. Always verify the rate directly with the bank before opening an account. Rates are variable and can change without notice.
Disclaimer
HYSACalc.com is for informational purposes only. Nothing on this site is financial advice. Consult a licensed financial advisor before making savings decisions.