What it means
Under the daily method, each day's interest equals the outstanding balance multiplied by the annual rate divided by 365, using the contract's actual convention. The monthly statement is the sum of those daily charges since the last payment, so months of different lengths produce different interest amounts.
Under the traditional monthly method, interest for a month is one-twelfth of the annual rate on the scheduled balance, so a payment made on the first or the fifteenth of the month, within the grace period, produces the same interest charge. Timing inside the month is irrelevant.
That difference cuts both ways. On a simple-interest mortgage, paying a few days late adds interest for each extra day, and the added amount comes out of the principal portion of the payment, while paying early, or paying more than due, reduces the balance sooner and stops interest from accruing on the repaid part.
At a constant balance the two methods can coincide, because a 365-day year of daily accrual at a given nominal rate sums to the same annual interest as twelve monthly accruals at that rate. Differences arise from payment timing, leap years and the exact day-count convention in the note.
Simple interest should not be confused with precomputed or add-on interest: the CFPB explains that precomputed interest is calculated up front and spread across payments, while simple interest is calculated on the actual outstanding balance, daily or monthly. With a precomputed loan, early payment may not reduce the total interest; with simple interest, it does.
The loan type suits disciplined payers, since borrowers who pay early or make extra principal payments can shorten the term and cut total interest, while borrowers who routinely pay late can pay more than under a monthly-accrual mortgage at the same nominal rate. Monthly statements deserve a closer read under daily accrual, because a longer month, a delayed payment or a leap day each raises the interest portion, and watching the principal line, not just the total payment, shows whether the schedule is on track.
Before signing, read the note's day-count convention, grace period and late-payment treatment. The same nominal rate does not guarantee the same total cost across accrual methods.
In practice
Real-world examples.
Example
A fictional $200,000 mortgage at 6% accrues about $32.88 per day. A payment ten days late adds roughly $328.77 of interest that will not reduce principal. The borrower sees a smaller principal reduction on the next statement.
Example
In a fictional 30-day month, daily accrual on $200,000 at 6% totals about $986.30. The traditional monthly charge at the same rate and balance is $1,000. The difference of $13.70 is small in one month but shows why statements under the two methods do not match line by line.
Example
A fictional borrower pays half the payment two weeks early every month. If the servicer immediately applies it to principal rather than holding it pending a complete payment, the earlier credit reduces future interest. The borrower confirms the servicer's handling in writing before relying on it.
Formula
Calculation
Daily interest = outstanding balance x annual rate / 365. For $200,000 at 6%, daily interest = $200,000 x 0.06 / 365, about $32.88.
Illustrative month: 30 x ($200,000 x 0.06 / 365) = about $986.30, retaining precision until the final rounding, versus $200,000 x 0.06 / 12 = $1,000 under monthly accrual. Over a constant-balance 365-day year both total $12,000. Inputs are fictional; the note's actual convention controls.
Month length changes the daily-accrual figure. A 28-day month costs 28 x $32.88 = about $920.55, a 30-day month about $986.30 and a 31-day month 31 x $32.88 = about $1,019.18, while the monthly method charges a flat $1,000 whatever the month.
Payment timing matters too. A payment that arrives 5 days late adds 5 x $32.88 = about $164.38 of interest, which is taken from the principal part of that payment. A borrower who sends an extra $5,000 of principal on day 1 of a year saves $5,000 x 0.06 = $300 of interest over the following 365 days, assuming the balance is otherwise unchanged.Case study
Seen in the real world.
This case study is fictional and illustrative. A borrower refinances into a simple-interest mortgage without noticing the accrual method. He keeps his old habit of paying on the fourteenth. His first statements show less principal reduction than expected, because interest accrues until each payment arrives. After reviewing the note, he moves payment to the first of the month and adds a small extra principal amount.
Within a year the balance sits below the monthly-accrual projection at the same rate. The gain came from timing and extra principal, not from a lower nominal rate. In numbers, paying 13 days later than necessary each month on a $200,000 balance at 6% meant 13 x $32.88 = about $427 of extra interest a month in his illustration, taken from the principal part of the payment. Moving the payment date removed most of that, and an extra $100 of principal each month trimmed the balance further, so his statements finally matched the schedule he had expected.
Watch out
Common mistakes.
- Assuming the grace period makes late payment free; daily accrual charges for every extra day.
- Confusing simple interest with precomputed or add-on interest, where early payment may not cut total interest.
- Comparing loans on nominal rate alone without checking the accrual method or the day-count convention.
Questions
People also ask.
Does paying early help on a simple-interest mortgage?
Yes. Interest stops accruing on principal as soon as it is repaid, so early or extra payments reduce total interest over the life of the loan.
Is the daily rate exactly the annual rate divided by 365?
Under a 365-day convention, yes. The note controls the actual convention, and leap years or other bases change the result.
Is a simple-interest mortgage the same as a biweekly mortgage?
No. Biweekly describes a payment schedule; simple interest describes the accrual method. They can appear together or separately.
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