How to use the Amex High-Yield Savings
- Enter your starting balance and the advertised APY.
- Add any recurring monthly deposit you intend to make.
- Set the time horizon in months or years.
- Compare the ending balance against a rival account's APY to see the real gap in currency, not percentage points.
How the calculation works
APY already expresses the effect of compounding over a year, so the monthly growth factor is (1 + APY)^(1/12) rather than APY ÷ 12. Using the simpler division slightly understates growth; on large balances over long horizons the difference becomes visible, which is why the annual-equivalent conversion is used here.
Two real-world caveats change the outcome. The rate is variable, so a headline APY can be cut days after you deposit — projections are scenarios, not promises. And interest is taxable in most jurisdictions as ordinary income, so the after-tax yield on a 4.3% account can land nearer 3% for a higher-rate taxpayer.
Balance = P × (1 + APY)^(n/12) + D × [((1 + APY)^(n/12) − 1) / ((1 + APY)^(1/12) − 1)]Source: APY definition per US Truth in Savings Act (Regulation DD) annual percentage yield calculation.
Worked example
A 12,000 balance at 4.30% APY with 400 added every month for two years.
- Monthly factor = (1.043)^(1/12) = 1.003515.
- Lump sum grows to 12,000 × (1.043)^2 = 13,054.
- Deposits of 400 accumulate to roughly 10,014 including interest.
- Total ≈ 23,068 against 21,600 contributed.
About 1,468 of interest over two years — before tax on the interest earned.
Frequently asked questions
Is APY the same as interest rate?+
No. The interest rate is the raw rate; APY folds in the effect of compounding, so it is always equal to or slightly higher than the nominal rate.
Can the rate change?+
Yes. High-yield savings rates are variable and typically track central-bank policy, so they move both up and down without notice.
Is the interest taxable?+
In most countries yes, as ordinary income in the year it is credited, unless the account sits inside a tax-sheltered wrapper.
Is a high-yield account safe?+
Balances at insured institutions are protected up to the local deposit-guarantee limit; above that limit, spread deposits across providers.
Last reviewed August 31, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.