The overdue invoice
$
%
Per
per month
How is it worked out?
days
Interest starts this many days after the due date.
$
Only if your terms say so, and where the law allows it.
What is owed
Days late
60
Annual rate
1.5% a month × 12
18%
Interest per day
Amount × annual rate ÷ 365
$2.37
Late interest
$142.03
Total to collect
$4,942.03
You can only charge interest or a fee that your customer agreed to in advance, in your terms or on the invoice. Limits differ by state and province. In Canada, a contract that states a rate per month must also state the equivalent yearly rate, or the Interest Act caps the interest at 5% a year. Works in any currency. General information, not legal advice.