Interest is money the bank pays you for letting them use your deposits
When you put money in a savings account, the bank lends that money to other customers as mortgages, car loans, and business loans. In exchange for the use of your money, the bank pays you interest—a percentage of your balance, calculated and added to your account on a schedule the bank sets. The more you have in the account and the higher the interest rate, the more you earn.
The bank's interest rate on your savings is almost always lower than the rate it charges borrowers. That difference is how the bank makes money. Your job is to find an account where the rate is high enough to make the effort worthwhile, because rates vary widely—from nearly zero at some big banks to 4% or higher at online banks and credit unions.
Key Takeaways
- Interest is calculated as a percentage of your account balance, and the bank adds it to your account on a schedule—usually daily, monthly, or quarterly.
- The annual percentage yield (APY) tells you the real rate you will earn over a year, including the effect of compounding.
- Compounding means you earn interest on your interest, which accelerates growth the longer money sits in the account.
- Rates change without notice, so a 4% account today might pay 2% in six months if the Federal Reserve cuts rates.
How the bank calculates the interest you earn
The bank takes your account balance, multiplies it by the interest rate, and divides by the number of days in a year. That gives you the interest earned for one day. The bank repeats this calculation every day, then adds all those daily amounts to your account on a set schedule—usually monthly or quarterly, though some accounts compound daily.
Example: You have $10,000 in an account paying 4% APY. The daily interest is roughly $1.10 per day ($10,000 × 0.04 ÷ 365). If the bank compounds monthly, it adds about $33 to your account at the end of the month. The next month, the calculation is based on $10,033, so you earn slightly more. This is compounding—earning interest on the interest you already earned.
The longer your money stays in the account untouched, the more compounding works in your favor. After one year at 4% APY, your $10,000 becomes $10,408. After five years, it becomes $12,167. You did nothing except leave it there.
Why APY matters more than the stated interest rate
Banks sometimes advertise a simple interest rate (like "4%") but what you actually earn depends on how often they compound. Annual Percentage Yield (APY) is the rate that accounts for compounding, so it shows the real return you will get over a year.
If two accounts both advertise 4% but one compounds daily and one compounds quarterly, the daily-compounding account will pay slightly more because you earn interest on your interest more often. The difference is small in a single year but grows over time. Always compare APY, not the stated rate, when choosing between accounts.
APY also assumes you do not withdraw money during the year. If you take money out, you lose the interest that money would have earned, and you also lose the compounding effect on that interest.
How changes in the Federal Reserve rate affect your savings
Banks set their own interest rates, but they follow the Federal Reserve's lead. When the Fed raises its benchmark rate, banks usually raise savings rates within weeks. When the Fed cuts rates, banks cut savings rates just as fast—sometimes faster.
This means a 4% account today might pay 2% in six months if the Fed cuts rates and banks follow. You have no control over this, and the bank does not have to notify you in advance. Check your account statements or log in to your bank's website to see if your rate has changed.
High-yield savings accounts at online banks and credit unions tend to raise rates more aggressively when the Fed raises, because they compete for deposits. Traditional big banks often lag behind. If you want to maximize earnings, you may need to move your money to a different bank when rates shift.
The difference between simple interest and compound interest
Simple interest is calculated only on your original balance. If you deposit $10,000 at 4% simple interest, you earn $400 per year, every year, no matter what. Your balance grows in a straight line.
Compound interest is calculated on your balance plus all the interest you have already earned. After year one, you have $10,400. In year two, you earn 4% on $10,400, which is $416. In year three, you earn 4% on $10,816, which is $432. The amount you earn each year increases, and your balance grows faster and faster.
Nearly all savings accounts use compound interest, usually compounded daily or monthly. This is why leaving money untouched for years can turn a modest balance into something noticeably larger. The longer the time horizon, the more compounding matters.
What happens to interest if you withdraw money early
If you withdraw money before the compounding period ends, you lose the interest that money would have earned. If you withdraw $5,000 from a $10,000 balance mid-month, the interest calculation for that month is based on the full $10,000, but you only keep the interest earned on the $5,000 that stayed in the account.
Some accounts charge a penalty for withdrawals, though this is rare in savings accounts. More commonly, you simply lose the interest. This is why savings accounts are best for money you do not plan to touch—if you need the money in three months, the interest you earn will be small anyway, and the real benefit of compounding only shows up over years.
How to find the highest-paying savings account
Interest rates vary dramatically. A big national bank might pay 0.01% APY while an online bank pays 4.5% APY on the same $10,000 balance. Over one year, that is the difference between $1 and $450.
Online banks and credit unions almost always pay more than traditional brick-and-mortar banks because they have lower overhead costs and compete aggressively for deposits. Money market accounts and certificates of deposit (CDs) sometimes pay more than regular savings accounts, but they come with restrictions—money market accounts may limit withdrawals, and CDs lock your money for a set term.
Check the current rates at online banks like Marcus, Ally, and American Express Personal Savings, as well as your local credit union. Rates change frequently, so the highest-paying account today might not be the highest next month. Set a reminder to review your rate every six months.
Frequently Asked Questions
How often does the bank add interest to my account?
Most banks compound and deposit interest monthly or quarterly, though some compound daily. Check your account agreement or bank website to see the schedule. Daily compounding means you earn slightly more because interest is calculated more frequently, but the difference is small in a single year.
Can I lose money in a savings account?
No. The bank cannot take money from your account without your permission. Your balance can only stay the same or grow. However, if inflation is higher than your interest rate, your money loses purchasing power—$10,000 earning 1% interest while inflation runs 3% means you can buy less with that money next year.
What is the difference between a savings account and a money market account?
Money market accounts often pay slightly higher interest but usually limit the number of withdrawals you can make per month. Savings accounts have no withdrawal limits. Both are insured by the FDIC up to $250,000 per account holder per bank, so both are equally safe.
Does interest get taxed?
Yes. Interest income is taxable as ordinary income. The bank will send you a 1099-INT form at the end of the year if you earned $10 or more in interest. You report this on your tax return. The higher your interest rate and balance, the more tax you owe on the earnings.
What happens to my interest if I move my money to a different bank?
You keep all the interest you have already earned. When you transfer money out, the bank calculates interest through the day you withdraw, adds it to your account, and then you move the full balance (original deposit plus all interest earned) to the new bank.