Daily Compound Interest Calculator

Daily compound interest adds interest to your balance once every day, so that the next day’s interest is calculated on a slightly larger amount. This “interest on interest” effect is the same idea behind all compounding — daily compounding simply applies it as often as a calendar allows, which edges out monthly or annual compounding for the same headline rate.

It is the natural model for high-yield savings, money-market accounts, and day-trading return projections, where gains are often credited and re-risked every single day.

With a fixed daily rate the balance grows as A = P(1 + r)^t, where P is the principal, r is the daily rate as a decimal and t is the number of days. When you enter an annual rate instead, it is first converted to a daily rate by dividing by 365, giving A = P(1 + r/365)^{365 × years}.

For example, $1,000.00 at 5% a year compounded daily for one year grows to about $1,051.27 — a touch more than the $1,050.00 you would get without compounding, because each day’s interest joins the balance and earns too. For that flat, non-compounding baseline, see the simple interest calculator.

The table below is produced by the same engine that powers the calculator above, with weekends included and full reinvestment. Notice the yearly interest rising even though the rate never changes — that is daily compounding at work.

How much does compounding daily actually add? Here is $10,000.00 at 5% for ten years under three frequencies. The balances are close, and the effective rate barely moves once you pass monthly — daily compounding is better, but the marginal gain over monthly is tiny. To model monthly, quarterly or yearly crediting with full contribution options, use the compound interest calculator.

The lesson: chase a higher rate before you chase a higher compounding frequency. A small bump in the rate outweighs the difference between monthly and daily compounding many times over.

The effective annual rate, or APY, converts a nominal rate plus its compounding into a single comparable yearly figure: APY = (1 + r/365)³⁶⁵ − 1. A 5% nominal rate compounded daily becomes about 5.13% APY. When you compare savings accounts, the APY is the honest number — it already bakes in the daily crediting that a bare “5%” hides. The APY calculator does this conversion for any rate and frequency.

Two controls make this calculator different from a plain compound tool. The daily reinvest rate decides how much of each day’s interest compounds versus how much is taken out as cash, and the include-weekends toggle lets you accrue on business days only. Together they cover everything from a fully-reinvesting savings account to a weekday-only trading account that withdraws part of its gains.

You will see daily compounding most often in high-yield savings accounts and money-market funds, where interest is accrued daily and usually credited monthly. It also underpins return projections for active strategies — day trading, forex and crypto staking — where a position’s gains are realised and re-risked every day. In those settings the reinvest-rate and weekend controls above let you model income you draw down as well as gains you leave to compound.

As always, real accounts differ in their day-count rules and rarely hold a rate constant, so treat these figures as an illustration rather than a guarantee.

Time is measured in calendar days, with months approximated as 30 days and years as 365. Real accounts vary in their day-count conventions, and rates rarely stay constant. Treat these figures as an illustration of the mechanics — not as a forecast or as financial advice.