The interest you earn depends on the bank's APY, how much you deposit, and how long the money sits there

The dollar amount you earn is not a mystery—it is a straightforward calculation. If you have $10,000 in a savings account earning 4.5% APY, you will earn roughly $450 in a year, assuming you do not add or withdraw money. The bank multiplies your balance by the annual percentage yield, divides by 12, and credits that amount to your account each month. The actual mechanics vary slightly by bank—some compound daily, some weekly—but the result is nearly identical for most accounts.

What changes the number is the APY itself. A $10,000 deposit at 0.01% APY earns $1 per year. The same deposit at 5.35% APY earns $535. That difference matters, and it is why the APY is the only number worth comparing when you are choosing between banks. The balance matters too: $50,000 at 4.5% earns $2,250 per year, while $5,000 at the same rate earns $225.

Most banks credit interest monthly, though some do it daily or quarterly. You do not have to do anything to receive it—the bank calculates and deposits it automatically. Once it lands in your account, it becomes part of your balance and earns interest on itself the next month. This is called compounding, and it is why leaving money untouched for years produces noticeably more than the straightforward math suggests.

Key Takeaways

  • Your earnings equal your balance multiplied by the APY, divided by 12 for a monthly payout—a $20,000 deposit at 4.5% APY earns about $75 per month.
  • The APY is the only number that matters when comparing banks, because it already accounts for how often interest compounds.
  • Interest compounds monthly at most banks, meaning each month's earnings get added to your balance and earn interest themselves.
  • Withdrawals reduce your balance when ready, so taking money out mid-month means you earn less interest that month.
  • Online banks typically offer higher APYs than brick-and-mortar banks, sometimes 10 to 15 times higher for the same deposit size.

How the math works with real numbers

Start with a concrete example. You deposit $25,000 into a savings account with a 4.75% APY. The bank divides 4.75% by 12 to get the monthly rate: roughly 0.396%. It multiplies $25,000 by 0.00396 and credits $99 to your account in month one. Your new balance is $25,099.

In month two, the bank calculates interest on $25,099, not the original $25,000. That earns you $99.39. The difference is tiny in month two, but over years it compounds into real money. After 12 months at 4.75% APY, your $25,000 has grown to $25,1,197.50—not $25,1,187.50, which is what straightforward multiplication would give you. That extra $10 came from compounding.

If you withdraw $5,000 in month six, your balance drops to $20,099 (plus whatever interest accrued that month). From month seven onward, you earn interest only on the smaller balance. This is why timing matters: withdrawing early in a month costs you less interest than withdrawing late in a month, because the bank has already calculated that month's payout.

Why APY varies so much between banks

The APY you see advertised is set by each bank based on what the Federal Reserve charges banks to borrow money. When the Fed raises its benchmark rate, banks can afford to pay you more. When it falls, so do savings account rates. But banks do not all move at the same speed or to the same degree.

Online banks typically offer higher APYs than traditional banks because they have lower overhead—no branches, fewer employees, less real estate. A brick-and-mortar bank might offer 0.01% APY while an online bank offers 4.5% for the same deposit. Both are real banks with FDIC insurance, so the difference is purely operational cost, not risk.

Some banks also tier their rates: a higher APY for larger balances, a lower one for smaller ones. A bank might offer 4.5% on balances up to $100,000 and 4.25% on anything above that. Read the fine print, because the rate you see advertised may not explore to your exact balance.

What happens if the APY changes

Banks can change the APY on savings accounts at any time without notice. If rates fall, your earnings drop when ready. If rates rise, your earnings increase. You do not have to do anything—the new rate applies automatically to your next interest payment.

This is different from a certificate of deposit (CD), where the rate is locked in for a set term. With a savings account, you have flexibility but no may provide. If you want to lock in a rate, you would move money to a CD, but you cannot withdraw it early without a penalty.

How to compare what different banks pay

The only comparison that matters is APY to APY. Ignore marketing language about "high-yield" or "premium" accounts—those are just names. Look at the actual APY number, confirm it applies to your balance size, and check whether it is a promotional rate that expires after a few months.

Some banks advertise a high APY for the first three months, then drop it to 0.5%. The fine print usually says this, but you have to read it. If you are moving $50,000 to a new bank, a promotional rate that expires in 90 days costs you real money. Calculate what you would earn under the permanent rate instead.

A spreadsheet with three columns—bank name, APY, and your projected annual earnings at your balance—takes five minutes to build and makes the choice obvious. At $30,000 balance, 4.5% earns $1,350 per year while 0.01% earns $3. That $1,347 difference is worth switching banks for.

Interest paid on money you add during the year

If you deposit $5,000 in January and another $5,000 in July, each chunk earns interest from the day it lands in the account. The first $5,000 earns interest for 12 months. The second earns it for only 6 months. The bank tracks this automatically—you do not have to do anything.

This is why regular deposits compound faster than a single lump sum. If you add $500 per month to a savings account, each deposit starts earning interest when ready, and the total grows faster than if you deposited $6,000 once a year. Over a decade, the difference is substantial.

Frequently Asked Questions

Do I have to pay taxes on savings account interest?

Yes. Interest earned on a savings account is taxable income. Banks send you a 1099-INT form each January if you earned $10 or more in interest during the year. You report this on your tax return. The amount is usually small unless you have a large balance or a very high APY.

What if I withdraw money before the end of the month?

You still earn interest for the days the money was in the account. Most banks calculate interest daily, so withdrawing on the 15th means you earn interest for 15 days that month. You do not lose the interest you already earned, but you earn less that month because the balance was lower for part of it.

Can I earn more interest by moving money between accounts?

No. Interest is earned on the balance in each account, not on how many accounts you have. Splitting $50,000 across five banks earning 4.5% APY earns the same total as keeping it in one bank—$2,250 per year. The only reason to split accounts is if you want insurance coverage above the FDIC limit of $250,000 per bank.

Why is my interest payment different each month?

Because your balance changes. If you withdraw money mid-month, that month's interest is lower. If you deposit money, next month's interest is higher. The bank recalculates based on your actual balance each day, so the payout varies slightly month to month unless your balance stays exactly the same.

Is there a minimum balance to earn interest?

That depends on the bank. Some banks pay interest on any balance, even $1. Others require a minimum, often $500 or $1,000. Check the account terms before you open it. If you fall below the minimum, some banks stop paying interest entirely until you bring the balance back up.