Tool
Late-payment interest calculator
Estimate the late-payment interest that accrues on a past-due balance, based on the agreed rate and the number of days overdue.
Accrued late-payment interest
—
On the past-due balance, as of the number of days indicated
Interest per day—
Past-due balance—
Balance + late-payment interest—
Assumptions & method
- Simple-interest calculation: interest = balance × (annual rate ÷ 360) × days overdue. This is the most common commercial convention (360-day year).
- Late-payment interest is distinct from ordinary interest and applies only to past-due balances, as agreed.
- An excessive late-payment rate may be deemed injurious or usurious interest and reduced by a judge (criteria of the First Chamber of the SCJN, Mexico's Supreme Court). This tool does not judge whether the rate is lawful.
- Informational estimate; the definitive calculation depends on the clauses of your contract.
Frequently asked questions
The essentials, in brief
What is the difference between ordinary and late-payment interest?
Ordinary interest is the price of the loan while it is paid on time. Late-payment interest is a penalty charged only when there is a delay, on the past-due balance. They are usually agreed separately in the contract.
Is there a legal limit on the late-payment rate?
There is no single numeric cap, but the First Chamber of the SCJN (Mexico's Supreme Court) has held that notoriously excessive interest is usurious and a judge may reduce it on their own motion, weighing factors such as the market reference rate and the type of transaction.
Does late-payment interest generate more interest?
It depends on what was agreed. Anatocism (charging interest on interest) has specific rules under commercial law. This calculator uses simple interest on the past-due balance, without compounding.
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