Savings interest calculator
Enter a starting balance, an optional monthly deposit, and a rate. Get the balance after any term, total interest earned, and a growth chart -- built for the "how much will my savings account earn" question specifically, with daily compounding assumed.
Set to 0 for a lump sum with no ongoing deposits.
The rate your bank advertises for the account.
Balance after this term
$12,977.48
Total deposited
$11,000.00
$5,000 starting + deposits
Interest earned
$1,977.48
Effective annual yield
4.602%
daily compounding assumed
Balance over time
How savings account interest is calculated
A savings account grows the same way any interest-bearing deposit does: interest is calculated on the current balance -- including any interest already credited -- and added back into that balance, so the next period's interest is calculated on a slightly larger number. With daily compounding, that crediting happens 365 times a year:
Balancetomorrow = Balancetoday × (1 + r/365)
where r is the account's nominal annual rate. Run that forward for a year and it's mathematically the same as the standard compound interest formula, A = P(1 + r/n)nt, with n = 365. A monthly deposit is added to the balance each month before interest keeps accruing on the new, larger total -- it doesn't earn its own separate interest track, it just joins the pool that's already compounding.
Worked example
$5,000 starting balance, $100 deposited at the end of every month, a 4.5% rate compounded daily, over 5 years:
| Starting balance | $5,000 |
| Total deposited over 5 years ($100/mo × 60) | $6,000 |
| Interest earned | $1,977.48 |
| Balance after 5 years | $12,977.48 |
The effective annual yield at 4.5% compounded daily is 4.602% -- almost identical to the nominal rate, since daily compounding is already very close to the continuous limit. Plug the same four numbers into the calculator above and it lands on the same balance to the cent.
Frequently Asked Questions
How much interest will my savings account actually earn?
It depends on your balance, the rate, and the time you leave it in -- but the shape is the same for every account: interest earned grows faster over time because you earn interest on interest already credited, not just on your original deposit. On $5,000 at a 4.5% rate compounded daily with no further deposits, that's $1,261.53 in interest over 5 years, landing at $6,261.53. Add $100/month and interest earned rises to $1,977.48, because there's more principal working for you the whole time, not because the rate changed.
Is it worth adding a monthly deposit instead of one lump sum?
Not "instead of" -- deposits and the lump sum both grow at the same rate, so a monthly deposit habit is additive, not a substitute for compounding. In the worked example above, the $100/month habit contributes $6,000 of your own money over 5 years but the account ends up worth $6,715.95 more than the no-deposit case -- the difference is $715.95 of extra interest earned on those deposits as they sit in the account.
Why does this calculator assume daily compounding?
Because that's how most U.S. savings and high-yield savings accounts actually credit interest -- daily accrual, even when the statement only shows a monthly or quarterly posting. If your account compounds differently (monthly, quarterly, or continuously), the difference in the final balance is small -- see the frequency comparison on the daily compound interest calculator -- but for an exact match to your own account terms, use the full compound interest calculator, which lets you pick the compounding frequency directly.
Need to pick a different compounding frequency, an annual (not monthly) contribution, or model inflation? The full compound interest calculator exposes all of those. Curious what your bank's advertised rate actually yields once compounding is applied? Try the APY calculator. Figures here are estimates for general education, not investment or tax advice.