Daily Interest Loan Amortization Calculator

This daily interest loan amortization calculator estimates the monthly payment and total interest for a fixed-rate loan using monthly compounding, then explains how daily interest can make an actual payoff balance differ. Enter the loan amount, annual APR and term to see the standard monthly-payment estimate; the formula does not model a lender’s daily-balance method.

Formula

This calculator uses the standard fixed-payment amortization formula, with interest compounded monthly at the APR divided by 12. It calculates the payment as:

Payment = P × r ÷ [1 − (1 + r)⁻ⁿ]

• P is the starting principal, in dollars.
• r is the monthly interest rate as a decimal: APR ÷ 1,200 when APR is entered as a percentage.
• n is the number of monthly payments: years × 12.

Total interest is calculated as monthly payment × number of payments − principal. The monthly payment is rounded to the nearest cent before total interest is calculated. This is a monthly-compounding model, not a daily accrual calculation.

Worked Example

Using the calculator’s defaults—$20,000 principal, 8% APR and a 5-year term:

1. Convert APR to a monthly decimal rate: 8 ÷ 1,200 = 0.0066667.
2. Convert the term to payments: 5 × 12 = 60.
3. Apply the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] = $405.53 per month, rounded to cents.
4. Calculate total interest using the rounded payment: ($405.53 × 60) − $20,000 = $4,331.80.

The calculator therefore displays a monthly payment of $405.53 and estimated total interest of $4,331.80.

Assumptions

• The APR is fixed for the entire term.
• Payments are equal monthly payments, made at the end of each monthly period.
• Interest compounds monthly at APR ÷ 12; daily accrual is not simulated.
• Fees, taxes, insurance, PMI and escrow are not included.

What Daily Interest Means

With a daily-interest method, interest accrues from day to day on the outstanding principal. A simplified daily calculation is principal × annual rate ÷ the lender’s day-count basis × days elapsed. The day-count basis and precise handling of payment dates depend on the loan’s contract and servicing method, so an APR alone is not enough to reproduce every lender’s balance calculation.

As principal is repaid, the balance on which interest accrues generally falls. The timing of payments can therefore matter: two payment dates separated by different numbers of days may produce different accrued interest, even if both payments fall within the same calendar month. A monthly amortization estimate smooths interest into regular periods and cannot show that day-by-day variation.

Using the Estimate and Reading Results

Enter the original amount borrowed, the annual APR stated for the loan, and the repayment term in years. The output is an estimated scheduled monthly payment and the interest implied by making that payment for every month of the stated term. It is not a quote or a current payoff amount.

• Use the loan’s APR, not a monthly percentage. The calculator converts the annual percentage to a monthly rate.
• Use the original principal, not the amount remaining after payments.
• Check whether the lender’s stated term is in years or months before entering it.
• For an adjustable rate, changing payment, interest-only period or irregular payment schedule, one fixed-payment result cannot represent the full loan.

Rounding creates small differences. The displayed payment is rounded to cents, and the displayed interest uses that rounded payment for all scheduled months. A lender may calculate interest daily, apply payments on specific dates, or handle the final payment differently; its schedule can therefore differ from this estimate.

Daily Interest Versus Monthly Amortization

“Daily interest loan amortization calculator” can refer to two distinct calculations. A full daily schedule needs the principal, rate, payment amounts, payment dates, day-count convention and rules for applying payments. This calculator instead estimates a conventional level monthly payment from principal, APR and term. It is useful as a baseline, but it cannot claim to reproduce a specific daily-interest loan without those additional details.

For a rough sense of daily accrual on a balance that stays unchanged, divide the annual rate by the applicable number of days in the year and multiply by the balance and elapsed days. For example, at 8% on $20,000, a simplified 365-day calculation for one day is $20,000 × 0.08 ÷ 365, or about $4.38. That is an illustration of one day’s interest on an unchanged balance, not the calculator’s monthly payment and not necessarily the lender’s exact method. Actual accrual may use a different day-count basis, and the balance can change when payments post.

Common Limitations and Questions to Check

A common misconception is that APR divided by 365 always gives the exact daily rate. It is only a simplified conversion; contracts may define accrual and day counting differently. Another is that the scheduled payment equals the amount needed to close the loan on any date. A payoff figure may include interest accrued since the last payment and other contract-specific amounts, which this calculator does not estimate.

For a closer comparison with a lender’s statement, look for the stated interest calculation method, the day-count basis, payment posting dates, and whether extra payments reduce principal immediately. Use the lender’s figures for an exact schedule or payoff calculation. This page provides general arithmetic, not personal financial advice.

Frequently Asked Questions

How do you calculate daily interest on a loan?
A simplified method is outstanding principal × annual rate ÷ the applicable days-per-year basis × days elapsed. The loan agreement or lender’s servicing method determines the exact basis and posting treatment.

Does this calculator calculate interest every day?
No. It estimates a level monthly payment using monthly compounding at APR ÷ 12. It does not create a daily balance schedule or reproduce a lender’s day-by-day accrual.

Why can a daily-interest payoff differ from this estimate?
Interest may accrue between payment dates, and the actual balance depends on payment timing, the lender’s day-count method, and the way payments are applied. This calculator also excludes fees and other charges.

Does paying earlier reduce daily interest?
If a loan accrues interest on its outstanding balance, the posting date and resulting balance can affect accrued interest. The exact effect depends on the loan terms and servicing rules; this calculator does not model extra or early payments.

Is APR divided by 365 the exact daily rate?
Not necessarily. It is a common simplified illustration, but the applicable day-count convention and calculation method must be checked in the loan documents or with the lender.

The result is an estimate, and the lender’s disclosure gives the exact figures.

Related

• Refinance vs Extra Payments Calculator
• Extra Principal Payments: How They Change Loan Costs
• Recast vs Extra Payments Calculator: Compare Payoff

in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Monthly payment | $ | p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2