Math Tools
Online Credit-Term Interest Calculator
Calculate the two distinct questions described by the legacy page: simple interest on a fixed balance and annualized cost of declining a cash discount.
Two meanings, separated clearly
Calculate a credit-term cost
Choose fixed-balance interest or the annualized cost of declining a cash discount.
Simple-interest estimate
Credit-term result
—Simple interest on a fixed balance; not an actual account statement.
Quick answer
How is credit-term interest calculated?
For a fixed balance, interest equals principal × annual rate × days ÷ day-count basis ÷ 100. Cash-discount terms such as 2/10, net 30 instead use annualized cost = discount ÷ (100 − discount) × day-count basis ÷ (30 − 10) × 100. Choose the mode that matches the agreement.
How to use this tool
- Choose simple interest or cash-discount cost according to the agreement or invoice wording.
- Enter the amount, rate or discount, relevant days, and the 365- or 360-day basis specified by the contract.
- Review the substituted formula, result, and warnings, then export to Print, Excel, PDF, or TXT if needed.
How the calculation works
Simple-interest mode converts money to integer satangs and percent to a 1,000,000 fixed scale, then calculates principal × rate × days ÷ (100 × dayBasis), half-up rounded to satangs. Cash-discount mode calculates discount ÷ (100 − discount) × dayBasis ÷ (netDay − discountDay) × 100 using BigInt, half-up rounded to at most 6 decimals. Choose the legacy-default 365-day basis or 360 only when specified by the agreement.
Examples
| Example | Input | Expected result |
|---|---|---|
| THB 50,000 balance | |
THB 739.73 interest and THB 50,739.73 total |
| THB 25,000 balance | |
THB 739.73 interest and THB 25,739.73 total |
| 2/10, net 30 | |
THB 2,000 discount, THB 98,000 early payment, and about 37.244898% annualized cost |
Limitations
- Amounts are THB 0.01–999,999,999,999.99, rates are 0–100%, and days are 1–36,500; results assume a fixed balance.
- Simple interest does not compound and excludes daily balance changes, interim payments, fees, taxes, penalties, and grace periods.
- Cash discount must be greater than 0 and less than 100%, with net day later than discount day; the result is not a regulated APR disclosure.
- A 365- and 360-day basis produce different results; the agreement, invoice, or statement is authoritative.
- Results are not a quote or credit, accounting, legal, or lender-certified advice.
Frequently asked questions
How do the two modes differ?
Simple-interest mode prices time on a fixed balance. Cash-discount mode annualizes the cost of paying the full invoice later instead of paying a discounted amount early. Their results are not interchangeable.
Should I use a 365- or 360-day basis?
Use the basis stated by the agreement or lender. The legacy default is 365 days, while some products use 360; the results differ.
Can this reproduce an actual credit-card charge?
Only as a fixed-balance estimate. Actual cards may use daily or average daily balances, compounding, transaction posting dates, multiple payments, fees, and grace-period rules from the account agreement.
Does the website store my balance or terms?
No. Calculation and file generation happen in your browser without sending the values to the server.
References
- Bank of Thailand — credit-card interest education Verified 2026-07-31
- CFPB — how card issuers calculate interest from daily balances Verified 2026-07-31
- Legacy THcount — credit-term interest calculator Verified 2026-07-31
Content and calculation method last reviewed: