Tool
Default interest calculator
Estimate the default interest that accrues on a past-due balance, based on the agreed rate and the number of days overdue.
Accrued default interest
—
On the past-due balance, over the number of days indicated
Interest per day—
Past-due balance—
Balance + default interest—
Assumptions & method
- Simple-interest calculation: interest = balance × (annual rate ÷ 360) × days overdue. This is the most common commercial convention (360-day year).
- Default interest is distinct from ordinary interest and applies only to past-due balances, as agreed.
- An excessive default-interest rate may be deemed unconscionable or usurious interest and reduced by a judge (criteria of the First Chamber of the SCJN, Mexico's Supreme Court). This tool does not assess whether the rate is lawful.
- Informational estimate; the definitive calculation depends on the clauses of your contract.
FAQ
The essentials, in brief
What is the difference between ordinary and default interest?
Ordinary interest is the price of the loan while payments are on time. Default interest is a penalty charged only when payment is late, on the past-due balance. They are usually agreed separately in the contract.
Is there a legal limit on the default-interest 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 default 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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