How to calculate savings account interest
Enter your balance and the APY your bank advertises — the calculator accepts APY directly and treats it as an effective annual yield, which is the correct interpretation. The standard formula for a lump sum is Ending balance = P × (1 + APY)^t, where P is your starting balance and t is years. Interest earned is simply the ending balance minus the starting balance.
Under the hood the calculator uses month-by-month compounding after converting the APY to an equivalent monthly rate, which matches how most savings accounts actually work. For a lump sum (no monthly deposits), the month-by-month result and the annual formula give the same answer to the cent when the APY is entered correctly.
Why APY is the right number to enter
Banks are required to advertise savings rates as APY because it is the standardized, apples-to-apples number that already reflects how often compounding occurs. A bank that compounds daily and one that compounds monthly can both truthfully advertise “4.50% APY” and your balance will grow identically at both — because APY is defined as the effective yield after one full year of compounding, regardless of frequency.
If you enter a nominal rate instead of an APY, the result will be slightly off — either too low (if the account compounds more than once a year) or exactly right (if it compounds annually). Always use the APY shown on the bank's website or account statement for accurate projections.
How much does your savings rate matter over time?
On short horizons the rate matters less. On a $10,000 balance over 1 year, the difference between 0.5% APY and 4.5% APY is about $400. Over 10 years the same gap grows to about $3,500. Over 20 years it is nearly $11,000 — more than the original deposit. Compounding means early decisions about where you park your savings have a larger effect than they initially appear.
The switch from a traditional bank (near 0.46% APY) to a top-tier HYSA (4–5% APY) is the simplest, highest-impact financial adjustment most people can make in an afternoon. No investment risk. FDIC insured. No fees. The HYSA calculator lets you model balances with monthly deposits as well.
If you have a savings target rather than a balance to grow, the savings goal calculator answers how long it takes to reach a goal amount — or what monthly contribution is needed by a given deadline.
Interest on large balances: a quick reference
At 4.50% APY, approximate interest earned over 5 years:
- $5,000 → about $1,231 in interest
- $10,000 → about $2,462 in interest
- $25,000 → about $6,155 in interest
- $50,000 → about $12,310 in interest
- $100,000 → about $24,618 in interest
Use the calculator above for the exact figure at your rate and time horizon. The numbers above assume lump-sum deposits with no withdrawals.
Frequently asked questions
How much interest will $10,000 earn in a savings account?
At 4.50% APY over 5 years, $10,000 earns about $2,462 in interest for an ending balance of $12,462. At 1% APY the same balance earns about $510. At a typical traditional bank rate of 0.46% APY it earns only about $232. The calculator above shows the exact interest for your balance, rate, and time period.
Is savings interest calculated monthly or annually?
Most savings accounts apply interest monthly even when they compound daily. The APY shown by your bank already accounts for the compounding frequency, so the dollar amounts you see on your statement reflect the bank's actual compounding. This calculator accepts the APY directly and converts it to an equivalent monthly rate, giving you results that match what a standard savings account produces.
Do I owe tax on savings account interest?
In the United States, savings account interest is taxed as ordinary income in the year it is earned, regardless of whether you withdraw it. If you earn more than $10 in interest during the year, your bank will issue a 1099-INT. The interest is added to your taxable income and taxed at your marginal rate. Tax-advantaged accounts like a Roth IRA let you shelter some growth from tax, but they have contribution limits and withdrawal rules.
What is the difference between simple and compound interest on savings?
Simple interest is calculated only on the original principal: Interest = P × r × t. Compound interest is calculated on the growing balance — each period, interest is added to the balance and then the next period's interest is calculated on that larger number. Modern savings accounts always use compound interest, which is why your balance grows faster over time than a straight-line projection would suggest. The difference between simple and compound becomes significant over 10 or more years.
How do I calculate how much interest I will earn?
Enter your balance, APY, and time period in the calculator above. For a quick estimate, the formula for a lump sum compounding annually is: Interest = Balance × ((1 + APY)^years − 1). At 4.5% APY over 5 years on $10,000: 10,000 × (1.045^5 − 1) = 10,000 × 0.2462 = $2,462. For more frequent compounding or monthly deposits, the calculator handles the math precisely.
Worked examples
Each example below shows inputs fed directly into the compound interest engine — outputs are computed at build time, not hand-typed.
$10,000 at 4.5% APY for 5 years
$10,000 lump sum at 4.5% APY with no additional deposits, held 5 years.
A $10,000 savings balance at 4.5% APY earns about $2,462 in interest over 5 years, growing to roughly $12,462. At the national average of 0.46% APY, the same balance earns only about $232 — a $2,230 difference from rate alone.
$25,000 at 4.5% APY for 10 years
$25,000 lump sum at 4.5% APY with no additional deposits, held 10 years.
A $25,000 balance at 4.5% APY earns roughly $13,800 in interest over 10 years, growing to about $38,800. The interest-to-principal ratio improves in the later years as the growing balance earns more each period.
Interest earned at 4.5% APY: starting balance × years
Each cell shows total interest earned for a lump-sum deposit at approximately 4.5% APY held for the given number of years. No additional contributions.
| Starting balance | 1 yr | 3 yr | 5 yr | 10 yr |
|---|---|---|---|---|
| $5,000 | $225 | $705 | $1,230 | $2,763 |
| $10,000 | $450 | $1,411 | $2,460 | $5,525 |
| $25,000 | $1,124 | $3,527 | $6,150 | $14k |
| $50,000 | $2,249 | $7,054 | $12k | $28k |
| $100,000 | $4,497 | $14k | $25k | $55k |
4.5% APY uses an equivalent nominal monthly rate of ~4.407%. Use the calculator above for exact figures at your current APY.
What affects your results
These inputs move the needle most — ranked by their leverage on the final balance.
Interest earned scales directly with balance — doubling the balance doubles the interest at any rate. For a savings interest question (no ongoing contributions), balance size is the primary lever after rate.
The APY determines how fast each dollar grows. The gap between a 0.46% traditional account and a 4.5% HYSA is about $4.04 per $100 per year — worth $404/year per $10,000. Over 10 years with compounding, the gap exceeds $4,000 per $10,000 balance.
Savings interest compounds — each year's interest earns its own interest in subsequent years. The compounding effect is modest on short horizons (1–3 years) but becomes significant past 5 years as the accumulated interest becomes a meaningful part of the base.
Key takeaways
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Enter the APY shown on your bank's website — not a nominal rate. APY is the standardized effective yield that already accounts for compounding.
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The quick reference section above gives typical 5-year interest amounts at 4.5% APY — use it to sanity-check the calculator result for common balances.
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For deposits plus ongoing contributions, the HYSA calculator models both together. For a target-based question, the savings goal calculator solves for time or monthly contribution.
More questions answered
How much interest does $100,000 earn in a savings account per year?
At 4.5% APY, $100,000 earns about $4,500 in the first year ($4,500 = $100,000 × 0.045). Over 5 years with compounding, the total interest grows to about $24,618. At a traditional 0.46% APY, the same balance earns about $460/year — a $4,040/year difference from moving to a high-yield savings account.
Is savings account interest simple or compound?
Modern savings accounts use compound interest — each period's interest is added to the balance, and the next period's interest is calculated on that larger balance. Simple interest only applies the rate to the original principal each period; compound interest applies it to the growing total. After a few years, the difference is meaningful: $10,000 at 5% for 10 years earns $5,000 simple but $6,289 compound.
Do I pay taxes on savings account interest?
Yes. In the US, savings account interest is taxed as ordinary income in the year earned, even if you do not withdraw it. Your bank sends a 1099-INT if you earn more than $10. Tax rates on interest income are your marginal federal rate (10%–37% depending on income bracket) plus state tax. High earners in high-tax states pay meaningful tax on HYSA interest — factor this into after-tax comparisons with municipal bonds or other tax-advantaged alternatives.