Daily Compound Interest Calculator

Choose Simple or Compound Interest

This daily compound interest calculator applies your annual rate to each day’s balance, including interest already added. Switch to simple interest to keep accrued interest separate. Both results use the same opening amount, movements and dates.

Moneysmart explains compounding as earning interest on the starting balance and interest already earned. Simple interest applies only to the amount earning or incurring interest. Here, dated movements change that amount as the period progresses.

Choose the annual rate basis supplied with your terms. A nominal rate gives a daily decimal rate of annual rate divided by 100 and the day denominator. An effective annual rate gives (1 + annual rate / 100) raised to the power of 1 / denominator, minus 1. Dividing an effective annual rate directly by 365 produces a different annual return.

Actual / 365 always uses 365. Actual / actual uses 366 for each day in a leap year and 365 otherwise. The tool counts calendar days, including weekends. Across a year boundary, it applies each day’s own denominator.

Record Each Balance Change

Enter each advance, deposit, repayment or withdrawal as a dated movement. Positive amounts increase the balance. Negative amounts reduce it. Use one line per movement, such as 2028-02-15, -1850, without a dollar sign or thousands commas.

The opening amount is the balance immediately before movements on the start date. Same-day movements are combined and applied before that day’s interest. The start date counts and the end date does not. A movement on the end date changes the closing amount but earns or incurs no interest within this period.

Simple interest accrues separately and never earns interest. A negative movement reduces principal, so enter only the principal part of a payment where the payment also settles accrued interest. Daily compound interest joins the balance after each day and becomes part of the next day’s opening amount.

Movements must keep both comparison balances at or above zero. A repayment or withdrawal that exceeds either balance is refused. Use a separate calculation when a loan becomes a deposit account or when a payment must be allocated between principal and separately accrued interest.

Compare Loan and Savings Scenarios

Use the loan agreement or savings terms to set the annual rate and its basis. These examples are fictional and use a nominal annual rate with actual / 365. Each example includes the start date and excludes the end date.

A fictional loan starts at $24,850 on 1 Feb 2028. A principal repayment of $1,850 takes effect on 15 Feb 2028. By 1 Mar 2028, the 29-day period produces $124 of daily compound interest and a closing amount of $23,124. Simple interest is $123, with a closing amount of $23,123.

For a fictional savings balance, enter $12,500 at 4.8% for the same dates and add a $1,200 deposit on 15 Feb 2028. Daily compound interest is $50 and the closing amount is $13,750. The deposit earns interest for 15 days, including its deposit date.

Daily mortgage interest often accrues between interest-posting dates. Select simple accrual for an interval where interest remains separate, if those are the supplied terms. Daily compounding assumes daily capitalisation. Fees, offsets and the lender’s actual posting and payment-allocation terms require separate treatment to reconcile a statement.

Check the Daily Rate

The daily rate appears in basis points so small rates remain readable. One basis point is 0.01%. The annual equivalents show the nominal rate and the effective rate produced by daily compounding. In actual / actual mode, those figures use the first day’s denominator. The daily workpaper shows any later rate change.

To solve for a constant daily rate, remove all movements and enter a positive target closing amount. For daily compounding, the rate is (target / opening) raised to the power of 1 / days, minus 1. For simple interest, it is (target / opening - 1) / days.

The solved rate uses the selected method and counted days. Its annual equivalents use 365 days and appear beside the results. This inverse calculation uses no entered annual rate. It cannot separate interest from intermediate cash movements, fees or changes in contractual rates.

Download the Interest Workpaper

Download CSV for every daily row, including opening balance, movements, day denominator and interest. The Excel-compatible formula sheet is also a CSV. Open it in Excel to recalculate the daily rate, interest and closing balance from the entered numbers.

Both files include the method, rate basis and endpoint convention. The formula sheet includes a running interest total. With simple accrual, the final balance plus that total reconciles to closing with interest. With daily compounding, interest is already in the closing balance.

The calculator keeps full precision until display. Estimated totals show whole dollars, while daily workpaper amounts show cents. Summing displayed rounded rows can differ from the total. Exports retain unrounded numbers and the formula sheet rounds nothing during calculation.

The fictional repayment and deposit examples span February in a leap year. Switching to actual / actual changes the daily denominator to 366. Inputs and downloads stay on your device and are neither uploaded nor saved in browser storage.

When Another Calculation Applies

Use the loan repayment calculator to calculate payment sizes or payoff time from an amortising schedule. An interest accrual does not establish a required instalment.

Keep contractual daily interest separate from statutory overdue-interest rules. The penalty interest calculator estimates overdue interest from supplied terms. Apply any statutory rate changes and legal counting rules that govern the actual debt.

Division 7A minimum yearly repayments use their own rules. This calculation supplies arithmetic for an entered scenario and does not establish a compliant loan agreement or a minimum yearly repayment.

Model an Overdraft Balance

Choose Overdraft to enter the amount drawn, facility limit and separate fees. Positive movements are additional drawings, and negative movements are repayments. The same workpaper applies to an entered business line of credit.

Interest applies to the positive drawn balance, including daily capitalised interest in compound mode. Unused credit earns or incurs no interest here. Available credit is the facility limit less the current drawn balance, floored at zero. The result flags the largest excess without limiting the calculation to the facility limit.

For a fictional four-day simple-interest period, start with $1,000 drawn at 10% against a $2,000 limit. Repay $1,000 before day two and draw $500 before day four. Interest is $0 when rounded to whole dollars. The workpaper retains the positive accrual, about 41 cents, and the closing amount with interest is $500.

Repayment timing changes interest because only one day accrues on the first drawing and one on the later drawing. The intervening zero balance incurs none. An entered $25 facility fee stays separate, producing interest plus fees of $25 when rounded.

In simple mode, available credit excludes separately accrued interest. In compound mode, capitalised interest consumes credit. Entered fees stay outside the drawn balance. Model fee capitalisation separately if the facility terms add fees to the debt. Unused-limit fees and lender-required minimum repayments must come from the facility terms.