The basic formula: multiply your balance by the rate, then divide by the number of times interest compounds per year

Savings account interest is money the bank pays you for letting them hold your money. To find out how much you'll earn, you need three pieces of information: your account balance, the annual percentage yield (APY), and how often the bank adds interest to your account (called the compounding frequency).

The simplest version works like this: if you have $1,000 in an account earning 4% APY and the bank compounds interest once per year, you earn $40 that year. That's $1,000 × 0.04 = $40. But most banks compound more frequently — monthly, daily, or even continuously — which means you earn a small amount of interest, then earn interest on that interest. That's why the real calculation is slightly more involved.

The good news: you don't have to do this math yourself. Your bank's website or app will show you exactly how much interest you've earned. But understanding how it works helps you compare accounts and know what to expect.

Key Takeaways

  • APY is the rate you'll see advertised, and it already accounts for how often interest compounds, so you can compare accounts directly.
  • Interest compounds when the bank adds earned interest to your balance, so the next period you earn interest on a slightly larger amount.
  • Daily compounding earns you more than monthly compounding with the same APY, because interest gets added more often.
  • Your bank's website or mobile app shows your earned interest automatically, so you can verify the math without calculating it yourself.

What APY means and why it matters more than the interest rate

Banks advertise two different numbers: the interest rate and the APY. The interest rate is the percentage the bank applies to your balance each compounding period. The APY is the total percentage you'll earn in a year, already accounting for compounding.

APY is the number you should use to compare accounts, because it shows the real return you'll get. Two accounts might have the same interest rate but different APYs if one compounds daily and the other compounds monthly. The daily-compounding account will have a slightly higher APY because you earn interest more often.

For example, a savings account might advertise "4.50% APY". That means if you keep $1,000 in the account for a full year without adding or removing money, you'll have $1,045 at the end of the year. The bank has already done the compounding math for you and expressed it as an annual yield.

How compounding frequency changes what you earn

Compounding is when the bank adds your earned interest to your balance, so the next time interest is calculated, you earn interest on the interest. The more often this happens, the more you earn — but the difference is usually small.

Here's a concrete example. Say you have $5,000 and the APY is 4%. If interest compounds once per year, you earn $200 ($5,000 × 0.04). If it compounds monthly, the bank divides the annual rate by 12 and applies it each month. You earn a little bit each month, and each month's interest gets added to your balance before the next month's calculation. Over the year, you earn about $204.08 instead of $200. The difference is small, but it's real.

Daily compounding earns slightly more than monthly compounding. Continuous compounding (which some online banks use) earns the most, though the difference from daily is usually less than a dollar per year on a typical balance. This is why APY matters: the bank has already calculated all of this and expressed it as a single number you can trust.

The formula if you want to calculate it yourself

If you want to see the math, here's the standard formula for compound interest:

Final Amount = Principal × (1 + (Rate ÷ Compounding Periods))^(Compounding Periods × Years)

Let's use a real example. You have $2,000, the APY is 5%, and interest compounds daily (365 times per year). You want to know how much you'll have after one year.

Final Amount = $2,000 × (1 + (0.05 ÷ 365))^(365 × 1) = $2,000 × (1.00013699)^365 = $2,102.54

So you earn $102.54 in interest. If you wanted to know how much you'd earn in just one month, you'd change the "years" part to 0.0833 (one month divided by 12). Most people don't need to do this — your bank statement will show the exact amount — but the formula shows why daily compounding beats monthly compounding.

Where to find your account's APY and compounding frequency

Your bank publishes this information in the account disclosure document, usually called a "Truth in Savings" statement or "Account Terms and Conditions". You can request this from your bank's website, ask at a branch, or call customer service.

The disclosure will list the APY, the interest rate, and how often interest compounds. It will also tell you the minimum balance required to earn that rate, because many banks pay higher APY only if you maintain a certain balance.

Your online banking portal or mobile app will also show your current APY and how much interest you've earned so far this year. This is the easiest place to check, because you can see it updated in real time as interest is added to your account.

Why your actual earnings might differ from the calculation

If you calculate interest based on a fixed balance and then check your account, the numbers might not match exactly. This usually happens for one of three reasons: you added or withdrew money during the year, the bank changed the APY, or you're looking at a partial year.

Interest is calculated on your balance at the time each compounding period ends. If you deposit $500 halfway through the month, that $500 only earns interest for the remaining half of the month. If you withdraw money, you lose interest on that amount for the rest of the period. Banks calculate this automatically, but it means your earnings won't match a straightforward formula based on a single starting balance.

Some banks also adjust their APY based on Federal Reserve decisions. If the rate goes up or down, your APY changes, and your earnings for the year reflect the average rate across all the periods when your money was in the account.

Comparing interest earnings across different accounts

To compare how much you'd earn in different accounts, use the APY and your expected balance. Multiply your balance by the APY to get a rough annual earnings figure. For example, if you'd keep $10,000 in an account with 4.5% APY, you'd earn about $450 per year.

This rough calculation works because APY already includes compounding. It won't be exact (the real amount will be slightly higher due to daily or monthly compounding), but it's close enough to compare accounts side by side.

When comparing, also check the minimum balance requirement. Some accounts offer high APY only if you maintain $25,000 or more. If you can't meet that minimum, the bank might pay you a much lower rate. Read the disclosure carefully to see what rate applies to your actual balance.

Frequently Asked Questions

Does my interest earn interest?

Yes, if your account compounds interest (which nearly all savings accounts do). The interest the bank adds to your account becomes part of your balance, so the next compounding period, you earn interest on that interest too. This is why APY is higher than the stated interest rate.

How often does interest get added to my account?

It depends on your bank. Most compound daily, some compound monthly, and a few compound quarterly or annually. Check your account disclosure or ask your bank. Daily compounding earns you slightly more, but the difference is usually small — a few dollars per year on a typical balance.

Can I lose money if interest rates go down?

No. Your balance never decreases because of interest rate changes. If your APY drops, you straightforward earn less interest going forward, but the money you already have stays in your account. You don't lose what you've already earned.

Why is my calculated interest different from what the bank shows?

The most common reason is that you added or withdrew money during the period. Interest is calculated on your balance at the time each compounding period ends, so deposits and withdrawals change how much you earn. Your bank's statement is always the correct number.

Is there a difference between interest rate and APY?

Yes. The interest rate is what the bank applies each compounding period. APY is the total you'll earn in a year, already accounting for compounding. APY is always the number to use when comparing accounts, because it shows your real return.