How to count days past due, correctly
Days past due is calculated by subtracting the invoice due date from today, in calendar days. Statutory rules in the EU, UK, US, Canada, and Australia all measure this in calendar days — including weekends and holidays. The day count begins the day after the due date and includes the day of payment.
Most disputes about "how late is this invoice?" come from confusion between the invoice date, the due date, and the payment terms. The due date is the cliff — anything after that, even by one day, is past due and can accrue late fees if your contract permits. The calculator above handles this correctly: enter the due date and today, and you get back the calendar count plus business days (excluding weekends) for context.
- Calendar days: including weekends and holidays. This is what the law uses.
- Business days: excluding Saturdays and Sundays. Used informally for "how many work days has my client had to pay this?"
- Day 1: the day after the due date. If due date is May 10, May 11 is "1 day past due".
- Stop counting: on the day payment arrives — that day still counts as past due.
Aging buckets and what they mean
The accounting profession groups overdue invoices into aging buckets — Current, 1–30, 31–60, 61–90, and 90+ days past due. Each bucket has a different statistical recovery rate and warrants a different collections strategy. The calculator above colour-codes your invoice into the right bucket and gives you the playbook for that stage.
Industry research (Atradius, Coface, and similar credit insurance firms) consistently finds that recovery rates fall sharply with age: ~94% of invoices in the 1-30 bucket are eventually paid; that drops to ~70% in the 31-60 bucket; ~58% in the 61-90 bucket; and below 30% past 90 days. The implication: every week of inaction in the 30-60 range materially lowers the probability you'll see the money.
- Current (0): no action. Send a "thanks, payment terms attached" note when the invoice arrives in the inbox.
- 1–7 (warm reminder): one polite check-in. Most clients self-correct here — assume oversight, not malice.
- 8–30 (active reminder): second reminder, mention the late-fee terms, restate the running total.
- 31–60 (firm reminder): third reminder with full breakdown. Offer a one-time waiver in exchange for immediate payment.
- 61–90 (formal demand): written demand letter via certified mail. Pause new work for the client. Decide on recovery path.
- 90+ (escalation/write-off): collections agency, small claims, or write-off and bad-debt deduction.
When statutory interest starts to accrue
In the EU, the Late Payment Directive (2011/7/EU) makes interest accrue automatically once an invoice is past due, even without a contract clause. The rate is the ECB reference rate plus 8 percentage points (~12.25% APR as of 2026). In the UK, the equivalent law (Late Payment of Commercial Debts Act 1998) gives 8% above the BoE base rate (~13.25% APR) plus a tiered fixed compensation of £40 / £70 / £100.
In the US, Canada, and Australia, statutory interest is not automatic — it accrues only if your contract explicitly permits it. The most common B2B clause is "1.5% per month" (approximately 18% APR), which is enforceable in nearly every state and province. Without a clause, you have no legal right to charge interest at all, regardless of how many days past due the invoice is.
- EU B2B: interest + €40 flat fee accrue automatically from day 1 past due.
- UK B2B: interest + £40-£100 tiered flat accrue automatically from day 1 past due.
- US/CA/AU: only if your contract has a late-payment clause. Otherwise, no interest can be claimed.
- Day 1 vs Day 31: statutory interest starts day 1, not day 31 — the "Net 30 grace period" is a myth.
How to use this with your reminder workflow
Run the calculator daily on every overdue invoice (or weekly if you prefer batched check-ins). The aging bucket tells you exactly which template to send and what tone to strike. We also link directly to the Late Fee Calculator and the Email Generator so you can compute the running total and produce a polite reminder in under a minute.
A common cadence: Day +1, send a friendly reminder with no late-fee mention. Day +7, second reminder with the late-fee clause and accrual rate. Day +14, third reminder with the full breakdown and offer to waive in exchange for immediate payment. Day +30, written demand letter. Most invoices are paid between the second and third reminder, before the math gets uncomfortable.
- Day +1: gentle reminder, no late fee mentioned. Goal: avoid friction.
- Day +7: second reminder with late-fee terms. Goal: warn that the cost is rising.
- Day +14: third reminder with full breakdown + waiver offer. Goal: close before 30.
- Day +30: formal written demand. Goal: create the paper trail required for legal recovery.
Common mistakes that cost you money
Three mistakes account for most of the lost revenue we see in freelancer/SMB billing: not knowing the exact day-count, waiting until day 30 to send the first reminder, and accepting partial payments without applying them correctly. The calculator above prevents the first; this page solves the next two.
Waiting 30 days to start chasing is a costly habit. Recovery rates drop sharply after the first reminder is sent — psychologically, the longer the silence, the harder it is to break. Send the first reminder within 7 days of the due date.
On partial payments: applying the payment to principal first (not interest) is wrong. Universal commercial practice is to apply payments to accrued interest and fees first, then to principal. This matters when the invoice rolls into a new month and you want the late fee to keep accruing on the unpaid balance.
- Don't wait 30 days: first reminder by day 7. Recovery rates fall fast after the first month.
- Always document delivery: email read receipts at minimum. Certified mail for invoices over $1,000.
- Apply partials correctly: interest and fees first, then principal.
- Track every interaction: a one-line log per email/call protects you if it ever goes to small claims.