Work out when an invoice is due and what a late payment costs. Enter the invoice amount, the invoice date and your payment terms, then the date it was paid (or leave it as today if it’s still open). The calculator shows the due date, days late, the late fee or interest, the total due and the effective annual rate of the fee. Below it, a second panel prices an early-payment discount such as 2/10 Net 30. Everything runs in your browser and nothing is sent anywhere.


Days are calendar days, weekends and holidays included. Monthly fees count each started 30-day period after the fee starts as a month.

Due date
Paid (or today)
Days late
How the fee is worked out
Late fee
Total due
Effective annual rate of the fee

Early-payment discount (same invoice amount and date as above)

Terms
Discount amount
Client pays if they take the discount
Discount deadline
Annualized cost of skipping the discount
Same, compounded

To keep on top of who owes you what, the Freelancer Invoice & Client Tracker (Excel and Google Sheets) works out invoice due dates from your payment terms, flags overdue invoices on its own, logs hours at each client’s rate, and shows invoiced vs. paid by month with a monthly tax set-aside. Not sure what to charge in the first place? Try the free freelance hourly rate calculator. And to know how much of each payment to keep for tax, there’s the quarterly estimated tax calculator.

To plan the tax side for the whole year, the Freelancer Quarterly Tax Planner 2026 (Excel and Google Sheets, $9) logs each payment and expense, works out the share of every dollar to set aside, the safe-harbor and full quarterly payments, and tracks what you’ve paid against the 2026 due dates.

Disclosure: the Freelancer Invoice & Client Tracker and the Freelancer Quarterly Tax Planner 2026 are our own paid products, and we earn the sale price if you buy one.

How the numbers are worked out

due date          = invoice date + terms (calendar days; due on receipt = 0)
days late         = date paid - due date (0 if paid on time)
no fee while        days late <= grace period
fee days          = days late (from the due date)
                    or days late - grace (from the end of the grace period)
months            = fee days / 30, rounded up (each started 30 days counts)
flat fee          = the flat amount, once
% per month       = invoice x rate x months
% per year, daily = invoice x rate x fee days / 365
% per month, compounding = invoice x ((1 + rate) ^ months - 1)
late fee          = the smaller of the fee and your cap
total due         = invoice + late fee
effective annual rate = late fee / invoice x 365 / days late
early-payment discount d/n Net N:
  discount        = invoice x d
  annualized cost of skipping = (d / (1 - d)) x (365 / (N - n))
  compounded      = (1 + d / (1 - d)) ^ (365 / (N - n)) - 1

Example: a $1,000 invoice dated Jan 31, 2026 on Net 30 is due Mon, Mar 2, 2026 (February 2026 has 28 days). Paid on Apr 1, it’s 30 days late: 1.5% a month comes to $15.00, and 18% a year charged daily comes to $14.79. On 2/10 Net 30 the client saves $20.00 by paying within 10 days, and skipping that discount costs them about 37.24% a year.

The effective annual rate shows what a fee really amounts to. A flat $25 fee on a $1,000 invoice paid 5 days late is 2.5% for 5 days, or 182.50% a year, which is the kind of number rules on late fees and interest tend to look at.

How to write late fee terms on an invoice

Put the terms in your contract or proposal before the work starts, and repeat them on every invoice. Clients rarely argue with a fee they agreed to up front; a fee that first shows up on an overdue invoice is much harder to collect.

  • Give the due date as a date. “Due March 2, 2026 (Net 30)” leaves less room for argument than “Net 30” on its own.
  • Say exactly how the fee works: a flat amount or a percentage, per month or per year, whether it compounds, when it starts, and any grace period.
  • Say what it applies to, usually the unpaid balance only.
  • Send a friendly reminder a few days before the due date and on the day it’s missed. Most late payments are forgotten invoices, not refusals.
  • Be consistent. If you waive the fee, say so in writing so it doesn’t become the new default.

Example wording, with numbers you should replace with your own: “Payment is due within 30 days of the invoice date. Balances not paid by the due date incur a late fee of [rate]% per month on the unpaid amount, starting [number] days after the due date.”

Legal limits on late fees and interest vary by US state and by country. Many places cap the interest rate you can charge, treat business and consumer customers differently, or only allow a fee the customer agreed to in advance. Check the rules where you and your client are, or ask a lawyer or accountant, before you set a rate. This page explains the math only and is not legal advice.

One example of how this differs by country: in the UK, a business paid late by another business can claim “statutory interest” of 8% plus the Bank of England base rate, but not if the contract sets a different interest rate, and can also claim a fixed debt recovery sum of £40, £70 or £100 depending on the size of the debt (checked on GOV.UK in October 2026: interest on late commercial payments and claiming debt recovery costs). For UK statutory interest, choose “% per year, charged daily” above and enter 8% plus the current base rate.

FAQ

What does Net 30 mean?

The invoice is due 30 calendar days after the invoice date. Net 15, Net 45 and Net 60 work the same way, and “due on receipt” means it’s due on the invoice date. Weekends and holidays count, so check whether the due date lands on a non-business day.

What does 2/10 Net 30 mean?

The client can take 2% off if they pay within 10 days; otherwise the full amount is due in 30 days. Skipping the discount means paying 2% more to keep the money 20 days longer, which works out to about 37% a year, so many businesses with cash on hand take it.

Is 1.5% a month the same as 18% a year?

Close, but not quite. Charged as simple interest, 1.5% a month for 12 months is 18%. If it compounds monthly, a year comes to (1.015)^12 - 1, about 19.56%. And “per started month” rounding means a payment 31 days late is charged two months at 1.5%.

Should I charge a flat fee or a percentage?

A flat fee is simple and easy to understand, but on large invoices it’s small and on very small invoices its effective annual rate can be very high. A monthly percentage scales with the invoice. Some people use the greater of the two; whichever you pick, put it in writing before the work starts.

Does a grace period mean the fee starts later?

It depends on your wording, which is why the calculator lets you choose. With “from the due date”, a payment one day past the grace period is charged for every day since the due date. With “from the end of the grace period”, only the days after the grace period count.

Choosing an invoicing app? Compare FreshBooks vs Bonsai vs HoneyBook vs Wave (2026): plan prices and card/bank fees.

More tools and guides: all guides and free tools.

Not legal or tax advice.