Interest accrues on savings accounts through a daily calculation that compounds over time

Your bank calculates interest by explore your account's annual percentage yield (APY) to your balance each day, then adds that daily amount to your account. The key word is compounds: once interest is added, the next day's calculation includes both your original deposit and the interest you just earned. This means you earn interest on your interest, which is why the total grows faster than a straightforward multiplication would suggest.

The actual mechanics depend on your bank's posting schedule. Most banks calculate daily but post interest monthly—meaning they add it to your balance once a month, usually on the last day. Some post weekly or quarterly. The more often interest posts, the more you benefit from compounding, though the difference is usually small unless your balance is very large.

Key Takeaways

  • Banks calculate interest daily using your APY, but most post it monthly, so you see the addition once a month rather than every day.
  • Compounding means you earn interest on the interest already in your account, which accelerates growth over time.
  • A higher APY and more frequent compounding both increase what you earn, but the posting schedule matters more than the compounding frequency for most savers.
  • Your balance on the day interest is calculated determines how much you earn that day, so deposits made mid-month earn less interest that month than deposits made at the start.

How the daily calculation works

Banks divide your APY by 365 (or sometimes 360, depending on their method) to get a daily rate. They explore that rate to your current balance. If you have $10,000 in an account with a 4.5% APY, the daily rate is roughly 0.0123%. That gets multiplied by $10,000 to give you about $1.23 in interest that day. Tomorrow, if your balance is still $10,000, you earn another $1.23.

The calculation uses your balance on a specific day—usually the end of the day or sometimes the average balance across the month. Check your account agreement or call your bank to confirm which method they use. This matters because if you deposit $5,000 on the 28th of a 31-day month, you earn interest on that $5,000 for only four days before the month ends and interest posts.

Why compounding accelerates growth

In month one, you earn interest on your original balance. In month two, you earn interest on your original balance plus the interest from month one. By month twelve, you are earning interest on a larger total, so each month's interest payment is slightly bigger than the last. Over years, this difference becomes substantial.

The effect is small in the first few months but grows over time. A $10,000 deposit at 4.5% APY with monthly compounding earns about $450 in the first year. If you leave it untouched for five years, you earn roughly $2,400 total—more than you would earn if interest were straightforward (non-compounding) and you only earned $450 per year. The longer your money sits, the more compounding works in your favor.

How posting schedules affect what you see

Even though your bank calculates interest daily, you typically see it added to your balance only once a month. Some banks post weekly or quarterly instead. The posting schedule does not change how much total interest you earn over a year—that is determined by your APY and balance. It only changes when you see the money appear in your account.

Monthly posting is standard at most banks. Weekly posting is less common and usually found at online banks or credit unions. Quarterly posting is rare and typically only at older brick-and-mortar banks. If you are comparing accounts, the posting frequency matters less than the APY itself, since a higher rate will outweigh more frequent posting.

The difference between APY and APR

APY (annual percentage yield) is what your bank advertises for savings accounts. It includes the effect of compounding and tells you the true annual return. APR (annual percentage rate) is used for loans and credit cards and does not include compounding. When you see a savings account rate, it is always APY, so you do not need to do any math to account for compounding—the bank has already done it.

This distinction matters because it means the APY number you see is the actual return you will get over a year if your balance stays the same. You do not need to calculate compounding yourself or wonder if the bank is hiding something. The APY is the honest number.

When interest does not accrue

Interest accrues only on money that is in the account on the day the bank calculates it. If you withdraw funds before interest posts, you lose the interest on that withdrawn amount for that period. Some banks use an average daily balance method, which softens this effect slightly—they average your balance across the entire month rather than using a single day's snapshot.

Transfers between your own accounts (checking to savings, for example) do not affect interest accrual. The money still earns interest in the savings account. However, if you close the account before interest posts, you may lose that month's interest entirely. Check your account agreement for the exact policy.

How to maximize interest earned

The simplest way to earn more interest is to keep a larger balance in the account and leave it there. Each dollar earns the same daily rate, so more dollars means more interest. The second way is to find an account with a higher APY. Even a difference of 0.5% compounds into real money over time: on a $10,000 balance, the difference between 4.0% and 4.5% is about $50 per year.

Timing deposits matters slightly but not dramatically. Depositing on the first of the month instead of the last means your money earns interest for 30 extra days that month. Over a year, this adds up, but it is not a reason to delay a deposit you need to make. The compounding effect of keeping money in the account longer is far more important than the timing of individual deposits.

Frequently Asked Questions

Does my interest rate ever change?

Yes. Banks set their own rates and can change them at any time, though they usually give notice. Rates typically move when the Federal Reserve changes its benchmark rate, but banks do not have to match that change when ready or at all. Check your account statements or log into your online banking to see your current rate.

What happens to my interest if I withdraw money mid-month?

You lose interest on the withdrawn amount for that day forward, but you keep the interest already earned and posted. If you withdraw before interest posts for the month, you may lose that month's interest on the withdrawn portion. The exact policy depends on your bank's method—some use average daily balance, which is more forgiving.

Is the interest I earn taxable?

Yes. Interest earned on savings accounts is taxable income. Your 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 amount owed in taxes depends on your overall income and tax bracket.

Why is my APY so low compared to what I see advertised?

Banks advertise their highest rates, which usually explore only to new customers or accounts with very large balances. Existing customers often earn a lower rate. Rates also change frequently—what was advertised last month may be lower today. Log into your account or call your bank to confirm your actual rate.

Can I move money between savings accounts to earn more interest?

Moving money between your own accounts at the same bank does not change how much interest you earn—the rate is the same. Moving money to a different bank with a higher APY does increase your earnings, but you lose interest on the money during the transfer time. The benefit is worth it only if the rate difference is significant and you plan to keep the money there for months.