How to use the Amex High-Yield Savings
- Enter the starting balance.
- Enter the APY as a percentage, checking the bank’s current advertised rate yourself.
- Enter the number of years.
- Read future balance and interest before tax, assuming no deposits or withdrawals and a constant APY.
How the calculation works
APY already includes compounding. For a constant annual effective rate, future balance is P × (1 + APY/100)^years. Interest is that balance minus P. Do not divide APY by a daily frequency and compound it again; that would double-count compounding.
The projection excludes deposits, withdrawals, tax and changing rates. Repeat with different APYs to compare scenarios rather than treat a forecast as guaranteed income. Matheculator is not affiliated with American Express.
Balance = P × (1 + APY/100)^years; Interest = Balance − PSource: Annual effective yield definition, US Regulation DD. User-supplied rate; no current bank-rate feed.
Worked example
An illustrative $10,000 deposit at a constant 4% APY for two years, with no additional deposits.
- Convert APY: 4/100 = 0.04.
- Balance = 10,000 × 1.04² = $10,816.
- Interest = 10,816 − 10,000 = $816.
$10,816 balance and $816 interest before tax. The 4% rate is an example, not a current Amex offer.
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.