Arrears Calculator

Why your arrears figure and the CMS's rarely match

Your number comes from arithmetic. Weekly rate, number of weeks, minus whatever actually arrived. The CMS number comes from a chain of separate calculation decisions, each with its own effective date, and a week only counts as unpaid once the liability for that exact week has been recorded on the system.

Four things cause most of the difference:

• Backdated recalculations. If the paying parent reported an income change, or an annual review landed late and was applied retrospectively, the weekly rate for a past period may have been rewritten. Your spreadsheet is still using the old rate for those weeks.
• Effective dates, not separation dates. Liability normally runs from the date the CMS accepted the application, not the date the relationship ended and not the date the first letter arrived. How far maintenance can be backdated covers the narrow exceptions.
• Payments applied to the wrong period. Money that arrives while a case is in transition often gets allocated to ongoing liability instead of to the arrears balance, or the reverse. The total paid looks right and the arrears balance still looks wrong.
• Collect and Pay fees sitting on top.The 20% surcharge added to the paying parent's bill is a fee, not maintenance. It does not increase what the receiving parent is owed. Both parents can see the split on the fee calculator.

Neither figure is automatically correct. The CMS record is the official one and it is the one enforcement acts on. It is also produced by a system with a documented history of allocation errors. Your job is not to prove your total is right. It is to show exactly which weeks the two versions disagree about.

Arrears never time out, and bankruptcy does not wipe them

Ordinary consumer debt usually becomes statute barred after six years of no acknowledgement and no payment. Child maintenance does not work that way. There is no point at which arrears become unenforceable because they got old. Balances built up under the old Child Support Agency in the 1990s are still legally owed and have still been pursued decades later, which is covered in more detail in the guide to CMS arrears time limits.

Bankruptcy does not help either. Maintenance is excluded from the debts a bankruptcy discharges and it is excluded from a Debt Relief Order. A paying parent can come out the other side of bankruptcy with credit cards and loans gone and the maintenance balance untouched.

What enforcement actually looks like, in order

The powers escalate. In practice the CMS works down this list rather than jumping to the bottom, and most cases never get past the first two rows because the first two do not need a court.

The two no-court options are the ones that matter most, because they are fast in theory and slow in practice. A Deduction from Earnings Order typically takes six to eight weeks to reach an employer once the decision to make one has been taken, then waits for the next payroll run. What a liability order really is explains why the court stage is more of a formality than a hearing on the merits.

When the CMS says the case is "with enforcement"

That phrase covers a lot of ground. It can mean a Deduction from Earnings Order has been issued to a named employer. It can also mean the case has been put in a queue while someone tries to trace where the paying parent works. Those two situations look identical on a phone call and produce very different results.

Ask for specifics and write down the answers:

1. Which enforcement action has been taken, by name.
2. The date it was taken and the date it was sent out.
3. Who it was sent to, employer or bank, without needing the account details.
4. What the next review date on the case is.
5. What triggers the next step if this one produces nothing.

If the answers are vague or the same review date keeps moving, that is a service failure rather than a legal problem, and the route for it is a complaint. Our complaint letter generator puts the case reference, the dates and the specific failures in the format the CMS responds to. If the internal process runs out or fifteen working days pass with no response, the Independent Case Examiner takes it from there, and after that the Parliamentary and Health Service Ombudsman through your MP.

How to challenge an arrears balance you think is wrong

Split the problem in two, because the routes are different and using the wrong one wastes weeks.

If the underlying calculation is wrong

This is a dispute about income, the number of qualifying children, shared care nights or the effective date. Request a mandatory reconsideration within one calendar month of the decision date. That deadline is real and late requests need a good reason. If the reconsideration goes against you, the appeal goes to the First-tier Tribunal (Social Entitlement Chamber), which is free, independent of the CMS, and decides the point itself rather than sending it back. The mandatory reconsideration tool checks whether you are still in time and drafts the request.

If the calculation is right but the balance is not

Missing payments, misallocated payments and duplicated liability periods are handled through the complaints process, not through appeal. This is where a month-by-month breakdown does the heavy lifting, because the fastest way to move a case is to point at a specific row and give the date, the amount and the reference of the payment the system has lost.

One thing worth knowing before a liability order hearing: section 33(4) of the Child Support Act 1991 bars the magistrates' court from questioning the maintenance calculation. The court checks that the calculation exists and that the amount is unpaid. Turning up to argue that the income figure is wrong will not work there. That argument belongs in a mandatory reconsideration, and it needs to have been started already.

Turning the breakdown into something a decision maker can use

A total on its own is easy to dismiss. A dated table is harder to ignore. Print the month-by-month output, then attach three things to it.

• Bank statements for the same period, with maintenance credits highlighted. Statements beat screenshots because they show the whole account, not just the entries that help you.
• The CMS calculation letters that set each weekly rate, so the rate used in each row can be traced to a decision.
• A one page covering note giving the case reference, the period in dispute, your total, the CMS total and the difference between them in pounds.

Keep the same figures across every document you send. If a complaint says one number and a tribunal submission says another, the discrepancy becomes the story instead of the arrears. And check the running total again after each annual review, because a changed rate rewrites part of your table.

This calculator gives you a defensible figure and a paper trail. It does not replace the CMS record and it does not carry any legal weight on its own. What it does is let you walk into every conversation knowing which weeks you are arguing about.

Common questions