Want to know how much your savings will actually earn each month? You do not need fancy software. One short formula does the whole job, and once you see it worked out, you can run the numbers on any account.
Below is the exact compound interest formula banks use, a step-by-step example with real dollars, and a simple table so you can plug in your own balance and rate. As of July 2026, this is all you need to estimate monthly savings interest. If you would rather skip the math, a HYSA calculator can project the same numbers for you.
The monthly compound interest formula
Most savings accounts compound interest monthly, meaning the interest you earn each month gets added to your balance and starts earning its own interest. The formula is:
A = P(1 + r/n)^(nt)
Here is what each letter means:
- A = the final amount (your ending balance)
- P = the principal (your starting balance)
- r = the annual interest rate, written as a decimal (5% becomes 0.05)
- n = how many times interest compounds per year (12 for monthly)
- t = the time in years
The interest you earned is simply A minus P. That is the whole thing. This is essentially how banks calculate interest on a savings account behind the scenes.
A worked example, step by step
Say you deposit $5,000 into a savings account paying a 5% annual rate (0.05) that compounds monthly (n = 12), and you leave it for one year (t = 1).
Plug the numbers in:
- Start with the monthly rate: 0.05 / 12 = 0.0041667
- Add 1: 1 + 0.0041667 = 1.0041667
- Raise it to the power of nt, which is 12 x 1 = 12: 1.0041667^12 = 1.051162
- Multiply by your principal: $5,000 x 1.051162 = $5,255.81
So after one year, your balance is $5,255.81. The interest you earned is $255.81.
How much lands in your account each month
For a rough monthly figure, the first month's interest is your balance times the monthly rate: $5,000 x 0.0041667 = about $20.83. The next month is slightly more because the base grew, and so on. That gradual increase is compounding at work.
A quick reference table
Here is what $10,000 earns in one year at a few common rates, compounded monthly:
| Starting balance | Annual rate | Ending balance (1 yr) | Interest earned |
|---|---|---|---|
| $10,000 | 1% | $10,100.46 | $100.46 |
| $10,000 | 3% | $10,304.16 | $304.16 |
| $10,000 | 4% | $10,407.42 | $407.42 |
| $10,000 | 5% | $10,511.62 | $511.62 |
Notice how much the rate matters. At 5% you earn five times what you earn at 1% on the same balance.
APY vs. interest rate: the shortcut
Banks advertise an APY (annual percentage yield), which already bakes in monthly compounding. If you only want the one-year total, you can skip the formula: just multiply your balance by the APY.
For example, $10,000 at a 4.07% APY earns about $407 in a year, which matches our 4% monthly-compounded result above. Use the full formula when you want to see growth month by month or over several years; use APY for a fast annual estimate.
Why the rate you pick is everything
The math makes one thing obvious: the interest rate does the heavy lifting. Moving from a near-zero legacy account to a high-yield savings account paying a competitive rate can turn a few dollars a year into hundreds. It is worth comparing the best high-yield savings account rates before you decide where to keep your money.
If you are ready to put your money somewhere that actually earns, a mobile-first account like Current pairs a spending account with savings features and an app that tracks your balance in real time. Terms and conditions apply, and rates can change.
Current Banking
Current Banking
Current is a mobile-first banking app with no monthly fee and no minimum balance. Members can earn up to 4.00% APY with a qualifying direct deposit of $200, receive direct-deposit paychecks up to 2 days early, and overdraft up to $200 fee-free.
Standout feature
4.00% APY on Savings Pods (with a $200+ qualifying direct deposit) plus paycheck up to 2 days early — both included on the standard account for free
Fees
Free
Pros
$0 monthly fee; up to 4.00% APY on Savings Pods with qualifying direct deposit; paycheck up to 2 days early;
Cons
No physical branches
Another popular option is Chime, which offers a savings account with automatic round-up transfers and no monthly maintenance fee. Automatic transfers grow your principal, and since the formula rewards a bigger P, small automatic deposits can meaningfully boost what you earn over time. Review current terms before opening.
Whatever account you choose, plug its rate into the formula above to see your own projected numbers.
Chime
Chime
- Fee-free banking plus early pay access - Overdraft up to $200 without fees - 5% cash back and build credit everyday. - 3.75% APY on your savings.
Standout feature
No credit check, no interest, no annual fee, and no minimum deposit required.
Fees
$0
Pros
Fee-Free Banking and Get paid up to 2 days early
Cons
App/online-only support, no branches
Your next steps
Grab your current savings balance and your account's APY or interest rate. Run them through A = P(1 + r/n)^(nt) with n = 12 to see your monthly and yearly earnings. If you want a refresher on how savings accounts accrue interest in the first place, that context makes the formula click faster.
Then do the same math with a higher rate you could realistically get. The difference in interest is the reason to shop around. Even a one or two point jump in rate compounds into real money over a few years.
Frequently Asked Questions
How do I calculate monthly interest on a savings account?
Use the formula A = P(1 + r/n)^(nt), with n = 12 for monthly compounding. Subtract your starting balance (P) from the ending balance (A) to find the interest earned. For a rough monthly figure, multiply your balance by the annual rate divided by 12.
What is the difference between interest rate and APY?
The interest rate is the base rate before compounding. APY (annual percentage yield) includes the effect of compounding over a year, so it is slightly higher. To estimate one year of earnings quickly, multiply your balance by the APY.
How much does $10,000 earn in a savings account?
It depends on the rate. At 1% compounded monthly, $10,000 earns about $100 in a year. At 5%, it earns about $512. The higher the rate, the more you earn on the same balance.
Does monthly compounding really make a difference?
Yes, though the effect grows with time and higher rates. Compounding adds each month's interest to your balance so future interest is calculated on a larger amount. Over many years, that snowball effect can add up significantly.
