Methodology

This page explains how CMS Help tools work and where they are limited.

How the estimator works

• Starts from the gross weekly income you enter (optional benefits tick-box).
• Applies a reduction for other children in the paying parent’s household (11% / 14% / 16%).
• Selects a CMS rate: nil, flat (£7), reduced, basic, or basic-plus (income above £800).
• Applies shared-care reductions for reduced/basic rates (52+ nights), with a £7 floor where rules require it.
• Shows the rate used, adjusted income, and rough weekly/yearly amounts.

Rate names summarised from GOV.UK: How child maintenance is worked out (last checked August 2026).

Assumptions

• Single paying parent and one active case.
• Stable income (no advanced handling for fluctuating self-employment or one-off spikes).
• No variation decision (unearned income, assets, special expenses) unless you adjust the figures yourself.
• Pension contributions are not deducted unless you reduce the income figure first.
• Default rates (where income is unknown) are not modelled.
• Collection fees are treated separately from the core amount owed — see Findings.

Letter builder standard

• Templates follow the usual CMS steps from GOV.UK / Citizens Advice: explanation → mandatory reconsideration → tribunal, and separately complaint → review → Independent Case Examiner.
• Signed-in users can save drafts privately to My Case.
• Exports use Word-compatible .doc and browser print/PDF.
• Drafts are guidance only — check deadlines and wording against your CMS letters.

Arrears check

• Compares the amount you think you should have owed (weekly × weeks) with total paid and CMS claimed arrears.
• Optional payment lines can fill the total-paid field and appear on the Excel download.
• The difference is an estimate — always ask CMS for their own line-by-line arrears breakdown.

Limits and disclaimer

• Estimator output is not an official CMS decision.
• A mismatch indicates a case for challenge, not proof by itself.
• Always request written breakdowns and source periods used in CMS decisions.
• CMS Help provides information support, not legal advice.

Evidence standard

• Prefer primary records: CMS letters, statements, bank evidence, court documents.
• Log dates and references for every event.
• Separate proven facts from assumptions.
• Redact identifying child and third-party details before sharing documents.

See the full checklist in Guides → Evidence.