How it works
Simple interest = unpaid principal × annual rate / 100 × overdue days / selected year-day basis.
Input definitions
- Unpaid invoice principal
- Enter the value in the labeled unit.
- Entered annual simple interest (%)
- Enter the value in the labeled unit.
- Overdue calendar days
- Enter the value in the labeled unit.
- Annual day basis
- Choose 365 / 360.
A worked example
- Unpaid invoice principal
- 1000
- Entered annual simple interest (%)
- 12
- Overdue calendar days
- 30
- Annual day basis
- 365
Assumptions & limits
Planning model using entered costs and policies, not country-specific law or a forecast. Use one currency and consistent time periods.
Sources & review
Maintained by AnsRio. Methods and examples use automated checks; this does not imply independent professional certification.
Method updated 2026-10-17. Content checked against the stated method and examples. Our verification approach.
Common questions
Does this automatically apply my country’s statutory late-payment rate?
No. You supply the annual rate, day basis and overdue days. It excludes statutory compensation, compounding, payment allocation and whether a late charge is legally enforceable.
How does Invoice simple interest from an entered rate work?
Simple interest = unpaid principal × annual rate / 100 × overdue days / selected year-day basis.
What are the limits of Invoice simple interest from an entered rate?
Planning model using entered costs and policies, not country-specific law or a forecast. Use one currency and consistent time periods.