This daily compound interest calculator shows what a deposit grows to when interest is added every day. Enter a starting amount, a rate, and a term. If you also save on a schedule, each contribution starts earning interest on the day it lands, not at the end of the year, which is where simpler calculators go wrong.
| Year | Opening | Contributions | Interest | Closing |
|---|
Daily compounding means interest is calculated on your balance every day, and each day's interest is added to the balance before the next day's interest is worked out.
Take $10,000 at 5%. The daily rate is 0.05 ÷ 365, so the first day earns $1.3699. That gets added to the balance. Day two then earns $1.3701, computed on $10,001.37 instead of $10,000. The gap is a fraction of a cent. It takes until day 28 before a single day's interest is a full cent higher than day one's.
The effect only becomes visible over time. After 30 days the balance is $10,041.18. One year in it is $10,512.67, against $10,500.00 if the same 5% were paid once annually, a difference of $12.67.
Stretch that to ten years. The same deposit reaches $16,486.65 with daily compounding and $16,288.95 with annual compounding, which is $197.70 apart on a $6,000-plus gain. Interest in the tenth year alone is $804.01, compared with $512.67 in the first year, because the balance earning interest has grown by roughly 60% in the meantime.
Every row below uses the same $10,000 at the same 5% for the same ten years. Only the compounding frequency changes.
The spread between annual and daily compounding is $197.70. Between monthly and daily it is $16.55. Monthly compounding at 5.0101% matches daily compounding at 5.00%, a rate difference of one hundredth of a percentage point. A monthly-compounding account paying 5.25% returns $16,885.24, which beats the 5.00% daily account by $398.59. The rate matters far more than the frequency.
| Compounding | Final balance | Interest earned | APY |
|---|---|---|---|
| Annually | $16,288.95 | $6,288.95 | 5.0000% |
| Quarterly | $16,436.19 | $6,436.19 | 5.0945% |
| Monthly | $16,470.09 | $6,470.09 | 5.1162% |
| Weekly | $16,483.25 | $6,483.25 | 5.1246% |
| Daily (365) | $16,486.65 | $6,486.65 | 5.1267% |
A = P(1 + r/n)nt
That formula covers the opening deposit on its own. Regular contributions need separate handling, because each one starts earning interest on the day it arrives and compounds for whatever time is left in the term. A deposit made in year two compounds for eight years, not ten.
The difference is not small. $10,000 at 5% compounded daily, plus $100 a month for ten years, reaches $32,022.28. Adding the same $12,000 of contributions at the end without compounding them gives $28,486.65. That understates the result by $3,535.63.
The annual rate is divided by the number of days in the year, and that daily rate is applied to the balance each day. The formula is A = P(1 + r/365)^(365t). Run $10,000 at 5% for ten years and you get 10,000 × (1 + 0.05/365)^3650, which comes to $16,486.65. Each day's interest joins the balance. The next day's interest is then calculated on a slightly larger number.
Better, but by very little. On $10,000 at 5% over ten years, daily compounding returns $16,486.65 and monthly returns $16,470.09. That is $16.55 apart. Frequency is worth far less than the rate. A monthly account at 5.25% would return $16,885.24 over the same period, so compare rates first and treat compounding frequency as a tiebreaker.
Two different things share this label. Changing only the compounding exponent barely matters. On $10,000 at 5% over ten years, the 365-day and 360-day results differ by about one cent. What actually moves the number is the bankers' method, where a lender divides the annual rate by 360 but charges interest for all 365 days. That raises the effective rate by 1.39%, so 5% becomes about 5.07% and $16,486.65 turns into roughly $16,601.
$10,512.67 after one year and $16,486.65 after ten years, with no further deposits. The equivalent figures for interest paid once a year are $10,500.00 and $16,288.95. Daily compounding is therefore worth $12.67 over the first year and $197.70 over ten. Regular contributions change the totals substantially. Adding $100 a month over the same ten years brings the balance to $32,022.28.
Many do, but the terms are worth reading carefully. Providers quote two separate things. One is how often interest is calculated (compounding), the other is how often it is paid into the account (crediting). An account can compound daily and credit monthly. If a provider advertises an APY, that figure already includes the compounding, so it is the number to compare between accounts.
The nominal rate ignores compounding. APY includes it. At 5% nominal, compounding annually gives an APY of 5.0000%, monthly gives 5.1162%, and daily gives 5.1267%. The nominal rate is identical in all three cases, so it cannot tell you which account pays more. APY can, which is why it is the figure to compare.