CMS Backdated Payments Calculator

The date your money actually starts from

Most people open this page believing the CMS can reach back into the past and recover the years a parent paid nothing. It cannot. Liability starts at the initial effective date on your case, and that date is normally the day the CMS makes contact with the paying parent, not the day you filled in the application.

That one sentence causes more anger about the CMS than almost anything else on the system. Understand it before you phone them, because it changes what you should be asking for.

Two dates, one gap

There is the date you applied. There is the date the CMS got hold of the other parent. Between them sits a gap you did not create and cannot control. The calculator above measures that gap and puts a figure on it, so you can see in pounds what the delay was worth.

The official position is that liability runs from the initial effective date. Where that date falls later than your application date, the difference is treated as money that was never legally due rather than a debt owed to you. Plenty of parents think that is wrong. It is still how the scheme is administered, and arguing the principle on the phone will not move the date.

Why there is no route around it

Section 8 of the Child Support Act 1991 removes the jurisdiction of the courts over child maintenance in most cases. That closes the obvious alternative. You cannot ask a family judge to order the past years that the CMS will not cover, because the judge has no power to make that order. A handful of exceptions survive, including school fees, expenses connected to a child's disability and top up orders where income sits above the CMS ceiling, but none of them repairs an ordinary gap in past payments.

So the practical advice is blunt. Apply early. Every week you wait is a week that will never be assessed. If you are weighing up whether to open a case at all, the main maintenance calculator will show you the weekly figure at stake, which is usually enough to settle the question.

Arrears are a completely different thing

Once an assessment exists, any week that goes unpaid becomes arrears, and arrears behave nothing like backdating. There is no time limit on collecting them. Child maintenance arrears are not statute barred, so the six year cut off that people remember from credit card debts and loans simply does not apply.

• Backdating looks backwards from your application. In almost every case it does not exist.
• Arrears run forward from your effective date. They do not expire, and they stay owed until paid or formally written off.

If your case already has an assessment and the payments stopped, you are dealing with arrears and your position is far stronger than it feels. The arrears calculator works out the running total from the assessment date so you have a figure to put in front of the CMS.

The one route that does create backdated liability

There is a real exception, and it is worth chasing. If the paying parent gave the CMS wrong income information, the CMS can revise the decision back to the original effective date. The corrected figure then applies from that earlier date, and the shortfall between the old assessment and the corrected one becomes arrears.

This is how genuine backdated liability gets created in practice. Not by arguing about the effective date, but by proving the income behind the assessment was wrong. Useful evidence includes payslips, P60s, company accounts filed at Companies House, dividend records and anything showing a standard of living the declared income cannot support. Where the income is structured through a company or drawn as dividends, the variation checker covers the grounds that apply.

A worked example of the gap

Take a paying parent on £500 gross a week with one qualifying child. One child sits at the basic rate of 12%, so the weekly figure is £60. Now put a nine week delay between the application and the initial effective date.

Two children would be 16% and three or more would be 19%, so the same delay costs more the larger the family. The rate itself depends on which band the income falls in: nil rate below £7 a week, a £7 flat rate from £7 to £100, a reduced rate from £100.01 to £199.99, the basic rate from £200 to £800, and basic plus above £800.01 where the excess over £800 is charged at 9% for one child, 12% for two and 15% for three or more. Gross weekly income above £3,000 is ignored entirely.

Two adjustments can pull the figure down before you get too attached to it. Other children living with the paying parent reduce gross income first, by 11% for one, 14% for two and 16% for three or more. Shared care then cuts the result by band: 52 to 103 nights a year removes a seventh, 104 to 155 removes two sevenths, 156 to 174 removes three sevenths, and 175 or more halves it and takes a further £7 per child per week.

Check your effective date before you argue

1. Find your first calculation letter. The initial effective date is stated on it, usually close to the weekly figure.
2. Compare it with the date your application was submitted. Keep the confirmation email or reference number if you have one.
3. Ask the CMS in writing to confirm the date the paying parent was first contacted. This is the date that actually drives everything.
4. Run the gap through the calculator above and keep the printed figure with your case papers.
5. Ask for a full payment history statement, which separates maintenance from any collection fees. The fee calculator explains how those fees change the totals on a Collect and Pay case.

If you think the date itself is wrong

An effective date that has been recorded incorrectly is a decision, and decisions can be challenged. Request a mandatory reconsideration within one calendar month of the decision. That step is compulsory. You cannot appeal to the First-tier Tribunal until the reconsideration has been decided. The mandatory reconsideration tool builds the request with the dates and reasons set out properly.

Delay is a separate problem with a separate route. If the CMS took months to contact the paying parent and never explained why, that is a service failure and belongs in the complaints process rather than an appeal. Complaints run through the internal stages first, then the Independent Case Examiner, then the Parliamentary and Health Service Ombudsman via your MP.

Once arrears exist, the powers are real

The enforcement ladder for arrears runs roughly in this order: a deduction from earnings order taken straight from wages, a deduction order taken from a bank or building society account, a liability order granted by the court, enforcement agents, and in the most serious cases disqualification from driving or commitment to prison.

Those powers are strong on paper. Getting the CMS to use them is often the harder part, and persistence in writing beats repeated phone calls. Every request logged in writing creates a record you can point to later.

Where the official position is contested

Two points deserve honesty. First, the effective date rule means administrative delay inside the CMS reduces the amount a child receives, and the parent who applied carries that cost with no remedy. Campaign groups and select committee evidence have criticised this for years. The rule has not changed.

Second, revision on the grounds of wrong income information is available in principle but uneven in practice. Cases involving self employment, dividends, retained company profit or unearned income frequently need pushing before anyone looks properly. Knowing the correct words to use makes a measurable difference, which is why the articles section sets out the wording and the regulations behind each request.

Use the number from the calculator as a starting position, not a promise. It shows what the delay was worth. Whether any of it converts into a recoverable sum depends on the effective date on your file and whether the income used was correct.

Common questions