How APY Works: Why 0.01% and 4% Both Look Small

Owen wants to move $5,000 into a savings account. One bank advertises a 0.50% APY, while another advertises 4.00%. The second number is clearly higher, but what does it actually mean? Will Owen get 4% every month? Is the rate guaranteed? Does the bank add all the interest at the end of the year?

In fact, the answer to all three questions is no. APY shows how much your money could earn over one year once compounding is included. It is a useful way to compare savings accounts, but it does not tell you everything about an account. In this lesson, we explain APY with simple dollar examples, look at what real banks pay and show why the percentage you notice is not always the one that matters.

What APY actually tells you

APY stands for annual percentage yield. It shows the yearly return on a deposit account, including both the interest rate and how often interest is added to your balance. In the United States, the Truth in Savings Act and Regulation DD set the rules for how banks must calculate and show it. As a result, every bank has to use the same method, which is exactly why APY is useful for comparing accounts.

For example, imagine you deposit $5,000 in an account with a 4.00% APY. If the rate stays the same, you leave the money and the interest in the account, and no fees are charged, you would earn about:

$5,000 × 4% = $200 in one year

Also, keep in mind that the APY is a yearly figure. A 4.00% APY does not mean you earn 4% every month. Instead, it describes what you would earn over a full year under those conditions.

Why 0.01% and 4% can look almost the same

This is where psychology comes in. To most of us, 0.01% and 4% both feel like “small percentages”. Our brains are not good at sensing the difference between small numbers that sit close to zero, so the gap between them looks minor. In dollars, however, it is huge:

Original Money Behaves calculation. Assumes the APY stays the same for the full year and there are no fees.

These are not made-up numbers. For example, the standard Chase Savings account and the standard Bank of America Advantage Savings account have paid around 0.01% APY in 2026, according to Bankrate. Meanwhile, the FDIC’s national average savings rate was about 0.38% in mid-2026. At the same time, several online banks, such as American Express and Ally, offered high-yield savings accounts paying roughly 3% to 4%. Rates change often, so always check the bank’s own website for today’s APY.

Why so much money stays in low-paying accounts

If the difference is this large, why do so many people leave their savings in accounts that pay almost nothing? One reason is the status quo bias: we tend to stick with the option we already have, even when a better one is available. Economists William Samuelson and Richard Zeckhauser documented this in their classic study Status Quo Bias in Decision Making.

Moving money feels like effort today, while the reward feels small and far away. On top of that, the account you opened years ago feels safe simply because it is familiar. As a result, the money stays put, and the lost interest never shows up as a bill, so it is easy to ignore. In contrast, a fee of $400 would get your attention immediately.

The fix is simple: look at your current APY, then turn the difference into dollars per year. If the gap is a few hundred dollars, it is usually worth one afternoon of setup.

APY and the interest rate are not the same

Although the interest rate and the APY are closely connected, they describe slightly different things. The interest rate is the basic rate used to calculate interest, while the APY shows the yearly result once compounding is included.

APY is for money you save. APR is for money you borrow.

Banks may add interest at different frequencies. For instance, one account may compound daily while another compounds monthly. Because of that, looking only at the basic interest rate can make comparisons harder, while the APY turns every account into the same yearly measure. So when you compare savings accounts, compare APY with APY. If you are dealing with a credit card or a loan, you need the APR instead, as explained in How Credit Card Interest Works.

What compounding means

Compound interest means that the interest you have already earned starts earning interest too. Imagine Owen deposits $5,000. During the first month, the bank calculates interest on that balance. Once the interest is added, the account holds a bit more than $5,000, so the next calculation uses the original deposit plus the interest already earned.

At first, the effect is small because the extra interest is only a few cents. Over longer periods, however, it becomes much more noticeable, especially when you keep adding money. Still, the APY itself does not assume you make new deposits. It only describes the yearly yield on the money already in the account.

A monthly compounding example

Let us look at an account with a $5,000 deposit, a 4.00% annual interest rate, monthly compounding, no new deposits, no withdrawals and no fees. The monthly rate would be about 4.00% ÷ 12 = 0.3333%. So in the first month, Owen would earn about $16.67, and his balance would become $5,016.67. Then, in the second month, interest is calculated on that slightly larger balance, which gives about $16.72.

Original Money Behaves calculation. 4.00% interest rate compounded monthly, no deposits, withdrawals or fees.

By the end of the year, Owen would have earned about $203.71. In other words, a 4.00% interest rate compounded monthly gives an APY of about 4.07%.

However, if a bank already advertises a 4.00% APY, compounding is already included in that figure. In that case, a steady $5,000 kept for a full year would earn about $200, so you should not add another “compounding bonus” on top.

How much difference the APY makes over time

Over one year, the gap between APYs is noticeable. Over several years, especially when you keep saving, it grows much larger. For example, here is $10,000 plus $100 a month for five years:

Original Money Behaves calculation. Assumes the APY stays the same for five years, monthly compounding, deposits at the end of each month and no fees or taxes.

Same savings, same habits, but a difference of almost $2,800. That said, savings rates are usually variable, so no one can promise a rate will stay the same for five years. Treat long-term examples as a way to see the size of the gap, not as a forecast.

Try it with your own savings

Use the calculator below to compare your current account with another APY. In short, it shows how much each one could earn on the same money over the same period.

How to use it: enter your current balance, how much you add each month and for how many years. Then type the APY you earn now and the APY of the account you are comparing. You can find your current APY in your banking app or on your bank’s website. The results update as you type.

Try changing only the monthly deposit, and you will notice something important: saving a little more each month often moves the result as much as a better rate. Both matter, and the best results come from combining them.

Why your real earnings may be different

The advertised APY is a standard way to compare accounts. However, it does not mean every customer will earn exactly the same amount. Here is why:

• Your balance changes. Interest is calculated on the money that is actually in the account, so withdrawals reduce it and money added late in the year earns less.
• The APY can change. Most savings accounts have variable rates, so an account paying 4.00% today may pay less in a few months.
• Some rates have conditions. For example, a bank may require a minimum balance, a direct deposit or a certain account tier to earn the top APY.
• Fees reduce what you keep. In fact, an account that earns $80 in interest but charges $120 in fees leaves you worse off.

A higher APY does not always mean a better account

APY matters, but it is only one feature. For that reason, you should also compare monthly fees, minimum balances, conditions for the top rate, how fast you can move money, and above all whether the bank is insured. Consider these two hypothetical accounts:

Hypothetical example.

Account B has the higher APY, but it also costs $120 a year. On a $2,000 balance, its 4.50% APY would earn about $90, which is less than the fee. Account A, on the other hand, would earn about $80 with no fee. So, in this case, the lower APY leaves you with more money.

Before you move money, also check that the bank is covered by FDIC deposit insurance, or by the NCUA for credit unions. We explain how that protection works in What Is FDIC Insurance, and how to work out your coverage across several accounts in How to Calculate FDIC Insurance.

Variable APY vs. fixed APY

Savings accounts usually have a variable APY, which can change after you open the account. On the other hand, certificates of deposit (CDs) usually offer a fixed APY for a set term, although taking the money out early often means paying a penalty.

General comparison. Each account has its own terms.

A variable APY gives you flexibility, but today’s rate is not a promise about the future. For that reason, any long-term calculation with a savings APY is an example, not a guarantee.

The opposite trap: chasing every small difference

Status quo bias keeps money in accounts that pay almost nothing. Yet there is also the opposite mistake. Once you notice rates, it is tempting to move your money every time another bank pays a little more.

On a $1,000 balance, a difference of 0.25 percentage points is only about $2.50 a year. On $20,000, the same difference is about $50. Moving money for tiny gains can leave you with extra passwords, forgotten accounts and transfer delays. Meanwhile, the amount you save each month usually matters much more. Adding just $25 a month puts $300 in your account each year, before any interest.

A sensible order is to pick an insured account with no avoidable fees, set up a regular saving habit, choose a competitive APY and then review it once or twice a year. If you are wondering whether your savings should be in an account at all, read Saving vs. Investing.

Next time you look at a savings rate, check this

Keep learning: What Is a High-Yield Savings Account?, Checking vs. Savings Accounts and What Happens If You Overdraft Your Bank Account.