Banking yield
calculator.
Compare the interest on savings at a big bank with a high-yield savings account. Set four inputs for a comparison in 30 seconds.
Full setup guide: Where to Bank and How to Structure Your Accounts
The question it answersHow much interest am I losing by keeping savings at a big bank instead of a HYSA?
Rules: United States. Data: savings rates are a September 2026 snapshot; check the bank's current APY. Privacy: runs in your browser. What you enter stays on your device unless you copy a share link, which puts your inputs in the link.
Interest is shown at the quoted APY (compounding already included). Tax on interest not included. Compares ongoing interest only, not promotional teasers. Current HYSA rates: verify before opening.
Projection, not a promise. The result follows the assumptions you enter. Real results will differ, sometimes by a lot.
What this tool assumes
- Big-bank savings APY ~0.01%. HYSA default 3.5%: a rough site estimate of what competitive online savings accounts pay (roughly 3 to 4%), not a published figure. Rates vary and track the federal funds rate; check the bank's current APY.
- For reference, the FDIC national rate cap on savings was 4.38% as of September 21, 2026[1]. It binds only banks that are less than well capitalized, so it is a reference point, not a ceiling for every bank.
- Interest is earned at the quoted APY. APY already includes compounding, so the result does not depend on how often the bank compounds.
Not financial advice. APYs change. Verify rates before opening accounts.
HOW THIS IS CALCULATED
This tool runs entirely in your browser: no data is sent to any server. It uses no live rates; both APYs come from the buttons and slider.
- Each APY becomes a monthly rate: r = (1 + APY)^(1/12) minus 1. Interest earned = balance × ((1 + r)^(years × 12) minus 1), which equals balance × ((1 + APY)^years minus 1). The balance stays fixed: no deposits or withdrawals.
- Money left on the table = HYSA interest minus current-bank interest over the years chosen (1, 3, 5 or 10; default 5).
- The per-year and per-month figures use the first year only: year-1 difference, and that ÷ 12.
- Current-bank presets are 0.01%, 0.05%, 0.50% and 1.00%, default 0.01%. For reference, the FDIC national average savings rate was 0.37% as of September 21, 2026[1].
- The HYSA slider runs from 1.5% to 6.0% in 0.1% steps with a default of 3.5%, a rough site estimate, not a published figure. For reference, the FDIC national rate cap on savings (it binds only banks that are less than well capitalized) was 4.38% as of September 21, 2026[1].
- The everyday comparison line is picked by the monthly difference as displayed, to the cent: over $200, $100, $50, $20 or $5. A gap shown as exactly $20.00 gets the line for over $5, not the one for over $20. At a $0 balance the line about moving the balance is left out.
- Dollar figures are rounded after the result is cleaned to the nearest millionth of a dollar, so a year-1 gap of exactly $523.50 shows as $524 and $43.63/month rather than falling a hair short in floating-point math.
- The balance slider runs from $0 to $100,000 in $500 steps. In a share link, a balance or HYSA rate outside its slider range or between its steps is moved to the nearest value the slider can hold, and a slider value that is not a number is replaced by the default ($15,000 balance, 3.5% HYSA rate). A current APY or year count that is not one of the preset buttons keeps the button already selected, which is the default (0.01% current APY, 5 years) on a fresh visit. A note above the results says what was changed.
Not modeled: tax on interest, rate changes during the period, promotional rates, balance minimums and fees. Verify the methodology or inspect the source code in your browser's dev tools.
Where to go from here
Sources
Bracketed numbers in the text link to these sources. Figures, rates and rules change: check each source’s date before acting on it.
- Federal Deposit Insurance Corporation, National Rates and Rate Caps. Checked 2026-09-26. ↩
Calculators are educational estimates, not financial advice. Disclosures · How pages are reviewed