Home › Free Tools › Free Late Fee Calculator for Overdue Invoices
Charging for a late payment? Enter the invoice amount, how many days it is overdue and your late-fee rule to see the penalty and the new balance due.
A common B2B standard is 1.5% per month (18% APR). Set late-fee terms on your invoice before the due date.
A late fee is a charge you add to an invoice when a customer pays after the due date. For a small service business or repair shop, it does two jobs: it nudges clients to pay on time, and it compensates you for the time and cash-flow hit of chasing overdue money. The two common structures are a flat fee (say $25 added once) or a monthly interest rate on the outstanding balance. A widely used B2B standard is 1.5% per month, which works out to 18% per year — this calculator handles both.
To use it, pick “Monthly interest %” or “Flat fee,” enter the invoice amount and the number of days the payment is overdue, then type your rate or flat amount. For the percentage option the tool prorates by day — 15 days late at 1.5% per month is charged as half a month — so a partially overdue invoice is not over-penalized. It updates as you type and shows the late fee, the days overdue, and the new total the customer owes.
A few practical rules keep late fees enforceable. State your late-fee terms on the invoice and in your contract before the work is done — a fee sprung on a customer after the fact is hard to collect. Keep the rate reasonable; many states cap the interest you can charge on overdue commercial invoices, so 1–1.5% per month is a safe, common range. A short grace period (5–10 days) before the fee kicks in also cuts disputes and keeps good customers happy.
StandupCRM tracks which invoices are overdue and can send automatic payment reminders, so you spend less time watching due dates and more time on the work. This free calculator is the quick way to work out a single late fee before you send the reminder.
Commonly a flat fee or 1–1.5% of the balance per month (about 12–18% a year). It must be stated in your invoice or contract beforehand, and some states cap the rate — check your local rules.
Multiply the overdue amount by your monthly rate and prorate for the days late, or add a flat fee. Enter the numbers above and this tool does it instantly.
Yes — 1.5% per month (18% APR) is a widely used standard for overdue B2B invoices. Many businesses also use a flat fee for small amounts.
Generally no. Put your late-fee terms on the invoice and in your agreement before the due date; retroactive fees are difficult to enforce.
Yes — free, no signup, and it runs entirely in your browser. Nothing you type is uploaded or stored.
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