Changes of circumstances and the annual review

A CMS calculation is not fixed. It is reviewed every year and can change in between if something important happens. Knowing the difference between a change and a challenge saves a lot of time.

Change or challenge?

If…	Then…
The decision was wrong when it was made	Ask for a mandatory reconsideration, then appeal
Something has changed since the decision	Report a change of circumstances. The CMS makes a new decision from the date of the change.

You can do both. If a decision was wrong and things have since changed, challenge the original decision and report the change separately.

Changes you should report

• The paying parent’s income changes by 25% or more (the government has announced this will fall to 15%)
• The number of nights of shared care moves into a different band
• A child leaves full-time education, turns 16 or 20, or goes to live with the other parent
• The paying parent starts or stops supporting other children in their household
• Either parent moves house or changes contact details
• Either parent starts or stops getting a benefit that affects the rate

Report changes as soon as you can. A change usually takes effect from the start of the maintenance period in which it is reported, not from the date it happened, so delay can cost money.

The annual review

Once a year, on the review date, the CMS gets the latest income figure from HMRC and recalculates. Both parents get a letter about a month before the new amount starts. Check it as carefully as the first calculation: the same one month time limit applies if you disagree.

Common questions

My income dropped by 20%. Will the CMS change the amount?

Not under the current 25% rule, until the annual review. Once the threshold falls to 15%, a 20% drop would be enough. Keep payslips ready.

The children now stay with me more. When does it count?

Tell the CMS as soon as the new pattern is in place and send evidence. It will usually look at the expected nights over the next 12 months.

Can a change be backdated?

Generally a change takes effect from when it is reported. There are limited exceptions. If you could not report it in time for a good reason, explain that in writing.