- 365/365 method
- An interest-accrual method, also called actual/365, that computes a daily rate by dividing the annual rate by 365 and charges it for each actual day. A full year’s interest equals the stated rate exactly, so there is no day-count premium. This calculator compares it with the 365/360 method to show the difference.
- Day-count convention
- The rule a loan uses to turn an annual rate into interest for a given period — which year length is the divisor and which days are counted. Common conventions are 30/360, actual/365 (365/365) and actual/360 (365/360). The same nominal rate produces different interest under each, so the convention belongs in any loan comparison.
- Daily rate
- The interest rate charged per day. Under 365/365 it is the annual rate divided by 365; at 6.5%, about 0.017808% a day. Multiplied by the balance and the days in the period, it gives the interest due. This calculator uses an average month of 365/12 days, which makes the monthly rate equal to the annual rate divided by 12.
- Nominal interest rate
- The stated annual rate in the loan documents, before accounting for the day-count method or compounding. Under 365/365, a year of simple interest equals the nominal rate. Two loans quoted at the same nominal rate can still cost different amounts if one of them accrues on a 360-day year.
- Effective annual rate
- The true yearly cost once monthly compounding is included. For a 6.5% nominal rate under 365/365, this calculator shows about 6.697%; the gap from 6.5% comes only from compounding monthly payments, not from the day count. The same loan under 365/360 would show about 6.793%, the difference being the day-count premium.
- 365/360 method
- A method, common in commercial lending, that divides the annual rate by 360 but charges it for all 365 days, making the true cost about 1.4% higher than the stated rate. The “interest saved vs 365/360” result shows what the same loan would cost extra under that method — about $552 on $100,000 at 6.5% over 10 years.
- Leap year
- A 366-day year. Under a strict actual/365 method, lenders handle it in different ways — some still divide by 365 and charge an extra day, others divide by 366. The effect is small but real. This calculator uses an average month of 365/12 days and does not model leap years.
- Amortization
- Paying off a loan through equal scheduled payments that each cover that period’s interest plus part of the principal, so the balance reaches zero by the last payment. Early payments are mostly interest; as the balance falls, more of each payment goes to principal. Under 365/365 the schedule matches a standard monthly amortization.
