Chart My Loan now supports two interest-calculation modes: monthly accrual and daily accrual.
Both models calculate interest using the outstanding principal balance, but they measure time differently. Monthly accrual treats each payment period as one-twelfth of a year. Daily accrual uses the actual number of calendar days between payments.
That difference may appear small during a single month, but it can affect the interest portion of each payment, the payoff date, and the total interest paid over the life of a loan.
What Is Monthly Interest Accrual?
The monthly model divides the annual interest rate by 12 to obtain a monthly rate.
Monthly interest = Principal balance × Annual rate ÷ 12
For example, suppose a loan has:
- A $25,000 principal balance
- A 6.5% annual interest rate
- Monthly payments
The first month's estimated interest would be:
$25,000 × 0.065 ÷ 12 = $135.42
Under this model, the length of the calendar month does not change the calculation. February, March, and April each count as one monthly period.
This is the traditional formula used by many online amortization calculators. It produces a clean schedule with a predictable monthly principal-and-interest payment.
What Is Daily Interest Accrual?
The daily model first calculates a daily interest rate and then multiplies it by the actual number of days in the accrual period.
Daily interest = Principal balance × Annual rate ÷ 365 × Days
Chart My Loan currently uses an Actual/365 model. That means it counts the actual calendar days between scheduled payments while dividing the annual interest rate by 365.
Using the same $25,000 balance and 6.5% rate, the daily interest amount is approximately:
$25,000 × 0.065 ÷ 365 = $4.45 per day
The interest for different payment periods would be approximately:
- 28 days: $124.66
- 30 days: $133.56
- 31 days: $138.01
Unlike the monthly model, the interest changes with the number of days between payments.
Monthly vs. Daily Accrual at a Glance
| Feature | Monthly accrual | Daily accrual |
|---|---|---|
| Time measurement | One-twelfth of a year | Actual calendar days |
| Basic formula | Balance × rate ÷ 12 | Balance × rate ÷ 365 × days |
| Effect of different month lengths | No effect | Interest changes with the number of days |
| Effect of payment timing | Usually not reflected within the monthly model | Earlier or later payments can change accrued interest |
| Best use | Standard amortization estimates and scheduled monthly loans | Loans whose contracts calculate interest using actual days |
Which Method Do Banks and Credit Unions Use?
There is no universal calculation method used by every bank or credit union. A single institution may use different methods for auto loans, mortgages, personal loans, student loans, credit cards, and home equity products.
The controlling information is found in the borrower's loan agreement and disclosures.
However, some broad patterns are common in the consumer lending market.
Auto Loans Commonly Use Daily Simple Interest
Daily simple interest is common for modern auto loans. Interest accrues on the unpaid principal balance, and a payment normally covers accrued interest before the remainder reduces principal.
The Consumer Financial Protection Bureau explains that simple interest is much more common than precomputed interest for auto loans. Simple interest may be calculated daily or monthly.
Several large banks and credit unions publicly describe daily simple interest calculations:
- Wells Fargo says its auto loans are simple-interest loans and that interest accrues daily.
- Chase explains simple auto-loan interest using the outstanding principal, a daily rate, and the number of days.
- Navy Federal Credit Union says it calculates auto-loan interest daily using the simple-interest method.
- Alliant Credit Union explains that interest on its simple-interest loans accrues daily.
These examples demonstrate a common industry practice, but they do not prove that every auto loan from every institution uses the same method. Always check the specific contract.
Mortgages Often Follow a Monthly Schedule
Traditional fixed-rate mortgages are commonly presented using a monthly amortization schedule. The annual interest rate is divided into monthly periods, and the scheduled principal-and-interest payment generally remains consistent.
That does not mean calendar days are irrelevant in every mortgage situation. Daily interest may still appear when:
- Interest is collected between closing and the first payment
- A borrower requests a payoff quote between payment dates
- A payment is late
- The contract uses a less common daily-interest structure
Home equity lines of credit can work differently from fixed-rate mortgages. A HELOC may calculate interest from an average daily balance or another contract-specific method.
Personal and Installment Loans Can Use Either Method
Personal loans, unsecured installment loans, and dealer-arranged loans vary by lender and contract.
A loan may use:
- Daily simple interest
- Monthly simple interest
- A standard monthly amortization formula
- Precomputed interest
Precomputed interest is different from both modes currently available in Chart My Loan. With that method, the lender calculates the expected interest in advance and incorporates it into the payment schedule.
According to the CFPB, precomputed interest is uncommon for auto loans, but borrowers should still check before assuming their loan uses simple interest.
Credit Cards Use a Different Model
The monthly and daily loan modes on Chart My Loan are intended for installment loans with a defined balance, rate, term, and payment schedule.
Credit cards typically use an average daily balance or another statement-cycle method. Purchases, payments, fees, grace periods, and different transaction APRs can all affect the calculation.
For that reason, a standard installment-loan calculator should not be expected to reproduce a credit-card statement exactly.
Why Payment Timing Matters With Daily Interest
Under daily simple interest, the number of days between payments directly affects the amount of accrued interest.
If more days pass, more interest accrues before the next payment. Therefore, a larger portion of that payment may go toward interest and a smaller portion toward principal.
Paying earlier may have the opposite effect. Fewer days of interest may accrue, allowing more of the payment to reduce principal.
The exact result still depends on the lender's rules, when the payment posts, and how additional payments are applied.
Which Mode Should You Select?
Select monthly accrual when:
- You want a traditional monthly amortization estimate.
- Your loan documents describe a monthly periodic rate.
- You are modeling a standard fixed-rate mortgage.
- You do not know the lender's exact method and want a simple baseline.
Select daily accrual when:
- Your contract says interest accrues daily.
- Your statement shows a daily interest or per-diem amount.
- You are modeling a typical daily-simple-interest auto loan.
- You want actual calendar days reflected in the estimate.
How to Find the Method Used by Your Loan
Review your promissory note, retail installment contract, Truth-in-Lending disclosure, or monthly statement.
Look for terms such as:
- Simple interest
- Interest accrues daily
- Daily periodic rate
- Per diem
- Monthly periodic rate
- Precomputed interest
- Actuarial method
- Rule of 78s
If the documents are unclear, ask the lender or servicer:
Does this loan calculate interest daily or monthly? What day-count convention do you use, and how do payment dates affect the interest charged?
Why the Calculator Results May Not Match a Statement Exactly
Even after selecting the correct mode, an online calculator may not reproduce a lender's statement down to the cent.
Differences can come from:
- The lender using 360, 365, or 366 days
- Payment posting dates
- Weekends and holidays
- Rounding rules
- Fees or optional products included in the balance
- Late, deferred, skipped, or partial payments
- Extra-payment processing
- An irregular first payment period
Chart My Loan provides an estimate based on the information entered. It does not have access to a lender's private servicing rules or transaction history.
Final Thoughts
Monthly and daily accrual are two different ways of estimating how interest builds on an outstanding loan balance.
Monthly accrual provides a clean, traditional amortization schedule. Daily accrual reflects the actual number of calendar days between scheduled payments and may more closely resemble many auto and simple-interest loans.
Neither mode is universally correct for every bank, credit union, or loan product. The correct choice depends on the specific contract.
Use the calculation method described in your loan documents whenever possible, and treat calculator results as estimates rather than lender payoff quotes.
This article provides general educational information and is not financial or legal advice.