It depends mostly on how old the debt is. Invoices a few weeks overdue often come in within a month of contacting every customer with an easy way to pay, while debts past 90 days usually need a decision, not more reminders. Stopping new invoices from going overdue can start straight away, but it takes a few months for the old balances to work through your aged debtor report.
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The short version
- Clearing a backlog and stopping new invoices going overdue are two jobs with different timescales.
- Recently overdue invoices often come in within a month of contacting everyone with an easy way to pay.
- Debts past 90 days usually need a decision: a court claim, a collection agency or a write-off.
- On business invoices you can add statutory interest and £40 to £100 compensation, even on old debts.
- Keep it under control with prompt invoices, direct debit for regulars and chasing on a schedule.
Two jobs with different timescales
When overdue invoices have got away from you, you've got two jobs: clearing the backlog that's already overdue, and stopping next month's invoices from joining it.
Stopping new ones is the quicker job. Once every invoice you send goes out with a clear due date, an easy way to pay and reminders on a fixed schedule, the flow of new overdue invoices tends to slow within the first month or two.
Your backlog takes longer, and how long depends on its age. A recently overdue invoice is often an admin problem: it went to the wrong person, it's waiting for approval, or it slipped down someone's list. An invoice six months overdue usually has a reason behind it, such as a dispute, a customer in difficulty or a customer who's decided to pay you last. Those need a conversation and a decision from you, and sometimes formal steps.
So before you start, sort the backlog by age and by customer. You'll see how much is recent and easy, how much is old and hard, and which few customers account for most of it.
A realistic timeline for clearing a backlog
Every ledger is different, but a plan along these lines should suit most small businesses. The weeks count from the day you start.
- First week: contact everything. Send every overdue customer a statement or a reminder with a payment link they can pay by card or pay by bank. Check you've got the right contact for each one. Some of your overdue money is likely to come in at this stage, simply because the invoice is finally in front of the right person.
- Weeks two to four: call the larger and older balances. Agree a payment date in writing, or an instalment plan if your customer can't pay in one go. Note any disputes and pass them to whoever in your business can resolve them.
- Months two and three: escalate what's still unpaid. For business customers, you can add statutory interest (8% over Bank of England base rate, so 11.75% a year at the moment), plus fixed compensation of £40 to £100 per invoice, even on invoices that are already old. A formal letter before action sets a final deadline. In England and Wales, the court's pre-action rules expect you to give at least 14 days, or 30 days where the customer is an individual or sole trader.
- From month three: decide. For each debt that's still unpaid, you'll need to choose between a court claim (in England and Wales you can start one online through the government's Money Claim service), a collection agency, or writing it off. Keep chasing anything that's still worth your effort, but stop counting on it in your cash flow forecast.
Done consistently, this tends to bring the recent part of a backlog down within the first month. The oldest debts take longer, because each one needs its own decision, and it's usually a few months before your aged debtor report looks clearly different.
What slows it down
A few things tend to stretch the timeline:
- Disputes nobody owns. A wrong amount or a missing purchase order won't be fixed by more reminders. It needs a credit note, a corrected invoice or a call.
- Wrong or missing contacts. Invoices you've sent to a general inbox, or to someone who's left, can sit unseen for weeks.
- No agreed terms. If you never agreed payment terms in writing, an invoice is legally late 30 days after the customer receives it, which can push back when your interest and compensation start.
- A routine that slips. It's common for a clean-up to start well and stall in your first busy fortnight. If chasing depends on you remembering, the backlog tends to grow back.
How to keep it under control afterwards
Once the backlog is down, keeping it down is mostly about routine. Get invoices out promptly, each with a clear due date. Agree how regular customers will pay before the work starts, ideally by direct debit, so those invoices are collected on the due date automatically. Decide in advance what happens at 30, 60 and 90 days overdue, so each step is already chosen when the date comes.
The chasing is the part that's easiest to hand over. Adfin sends invoices with a payment link and collects by card, Apple Pay, Google Pay, pay by bank, bank transfer or direct debit. You set the rules, and its AI Customer Agents work within them: reminders by email, SMS or WhatsApp at the intervals you choose, a statement when a customer goes quiet, instalment plans for customers who need them, and statutory interest on overdue business invoices if you switch it on. Payments are matched to their invoices in Xero or QuickBooks, so your aged debtor report stays accurate while you work through what's left.
Common questions
How long does it take to clear a backlog of overdue invoices? Recently overdue invoices often come in within a month of a clear reminder with a payment link. Debts past 90 days take longer, because each needs a decision.
Can I add interest to invoices that are already overdue? On business invoices, yes. Statutory interest runs from the day after the due date, so you can claim it on older invoices, plus fixed compensation of £40 to £100 per invoice.
When should I send a letter before action? Once reminders and calls haven't worked, usually somewhere between 30 and 90 days overdue. Give at least 14 days to respond, or 30 days if the customer is an individual or sole trader.
Should I offer an instalment plan on an old debt? If the customer can't pay in one go, an agreed plan in writing can be quicker and cheaper than a court claim. Set out the dates and amounts clearly.
When should I write off an overdue invoice? When the cost of recovering it is likely to be more than you'd get back, or the customer has become insolvent. Your accountant can advise on the tax treatment.
How do I stop invoices going overdue again? Agree payment terms and method before the work starts, send every invoice with an easy way to pay, and chase on a fixed schedule.
Sources
- GOV.UK - Late commercial payments: charging interest and debt recovery (accurate as of October 2026) https://www.gov.uk/late-commercial-payments-interest-debt-recovery/charging-interest-commercial-debt
- GOV.UK - Late commercial payments: when a payment becomes late (accurate as of October 2026) https://www.gov.uk/late-commercial-payments-interest-debt-recovery/when-a-payment-becomes-late
- Ministry of Justice - Pre-Action Protocol for Debt Claims (accurate as of October 2026) https://www.justice.gov.uk/courts/procedure-rules/civil/pdf/protocols/debt-pap.pdf
- Ministry of Justice - Practice Direction: Pre-Action Conduct and Protocols (accurate as of October 2026) https://www.justice.gov.uk/courts/procedure-rules/civil/rules/pd_pre-action_conduct
- GOV.UK - Make a court claim for money (accurate as of October 2026) https://www.gov.uk/make-court-claim-for-money
- Adfin - Credit control (accurate as of October 2026) https://www.adfin.com/credit-control
