High-Yield Savings (APY) Calculator
Project a high-yield savings balance from a quoted APY, a starting balance, and monthly deposits, and see why the compounding frequency does not change the annual yield.
A high-yield savings account quotes an APY, the annual percentage yield, which is the effective yearly return after compounding is included. This calculator projects your balance from a starting amount and monthly deposits at that APY. Because the APY already reflects compounding, the ending balance is the same whether interest posts daily or monthly; the frequency only changes the size of each posting, which the calculator shows as the per-period rate.
Assumptions
- The rate you enter is an APY (annual percentage yield), which already includes the effect of compounding. Because of that, the ending balance does not depend on the compounding frequency you pick: daily, monthly, and annual posting all reproduce the same APY and the same yearly growth. The frequency only changes the per-period rate, which the calculator shows so you can see the relationship.
- The starting balance grows at the APY for the number of years. Monthly deposits are made at the end of each month and grow at the exact monthly rate that reproduces the APY. The number of years is treated as a whole number.
- The APY is assumed constant for the whole period. In reality, savings rates are variable and banks change them as market rates move, so a real balance will differ as the rate does.
- Daily compounding uses a 365-day year. All figures are nominal (not adjusted for inflation) and before any taxes. Interest from a savings account is generally taxable, which this does not model.
- Not modeled: rate changes over time, taxes on interest, account fees or minimum-balance requirements, and inflation. Every result is rounded to the nearest cent.
- This is an estimate for educational purposes only, not financial advice. Savings rates change, so treat the projection as a snapshot at the current APY.
How it works
A high-yield savings account quotes an APY, the annual percentage yield. The APY is the effective yearly return after compounding is already included, which is the key to reading this calculator.
The starting balance grows at the APY: starting times (1 + APY)^years.
Monthly deposits grow as an annuity at the monthly rate that reproduces the APY,
(1 + APY)^(1/12) − 1, using the standard annuity future-value formula.
The compounding frequency you pick (daily, monthly, quarterly, annually) sets the per-period rate via
(1 + APY)^(1/m) − 1, where m is the number of periods per year. But because the APY already accounts
for compounding, every frequency reproduces the same annual yield, so the ending balance does not
change with the frequency. What changes is the size of each posting, which the calculator reports as
the per-period rate.
Worked example
Start with $10,000, add $200 a month, at a 4.5 percent APY, for 5 years.
- The $10,000 grows to $10,000 times 1.045^5 = about $12,461.
- The $200 monthly deposits grow as an annuity at the monthly effective rate (about 0.3675 percent) to about $13,399.
- Final balance: about $25,860.
- Total deposited: $10,000 + ($200 times 60) = $22,000.
- Interest earned: about $3,860.
Switch the compounding frequency from daily to monthly to annual and the final balance stays $25,860; only the per-period rate changes (a tiny daily rate, or the full 4.5 percent posted once a year). That is the point: once a rate is quoted as an APY, the frequency no longer changes the annual result.
Scope and limitations
The APY is assumed constant, but real savings rates are variable and banks change them as market rates move, so a real balance will differ. All figures are pre-tax and nominal; savings interest is generally taxable, and inflation erodes the real value, which you can check with the inflation calculator. This is an estimate for education, not financial advice.
Sources
- Consumer Financial Protection Bureau: what is APY and how compounding works
- FDIC: deposit insurance and savings accounts
- Truth in Savings (Regulation DD) defines APY as the standard, compounding-inclusive yield measure.
Frequently asked questions
- What is APY, and how is it different from interest rate?
- APY, the annual percentage yield, is the effective yearly return after compounding is included. A nominal interest rate does not include compounding, so the APY is slightly higher than the stated rate when interest compounds more than once a year. Banks advertise savings accounts by APY, which is what this calculator uses.
- Does compounding daily really beat compounding monthly?
- Not when the bank quotes an APY. The APY already bakes in the compounding frequency, so daily and monthly posting at the same APY grow your money identically over a year. More frequent compounding only matters when you are comparing nominal rates; once it is expressed as an APY, the frequency no longer changes the annual yield.
- Will my balance really grow this smoothly?
- Probably not exactly. High-yield savings rates are variable, and banks raise or cut them as market rates move, so your real APY will change over time. The projection assumes today's APY holds for the whole period, which is useful as a snapshot but will drift as rates change.
- Is the interest taxable?
- Generally yes. Interest from a high-yield savings account is usually taxable as ordinary income in the year you earn it, and the bank reports it if it is above a small threshold. This calculator shows the pre-tax balance, so your after-tax result will be somewhat lower depending on your tax rate.
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New to this topic? Our companion guide explains it in plain language: How Much Should You Have in an Emergency Fund?
Last reviewed June 2026.