Statutory Gross Assessable Income Auditor 2026 CMS 2012 Regulations 34-37 • RTI Feeds & Allowances Scheme: CMS 2012 Gross Income Scheme

Child Maintenance Income Calculator

Calculate your exact gross assessable income for child maintenance under CMS 2012 rules, including overtime, bonuses, and allowable deductions.

Features real-time HMRC RTI data stream simulation, taxable benefit evaluations (P11D), redundancy pay exemptions, and pension deductions.

RTI Gross Inflow Auditor

Gross Assessable Income & Allowances Calculator

Aggregates salary, bonuses, overtime, benefits in kind, and statutory deductions

HMRC RTI Model

Base Annual Salary (£)

Basic contractual gross earnings

Bonuses & Overtime (£/yr)

Taxable bonus / shift overtime

Pension Relief (£/yr)

100% deduction from gross earnings

Total Gross Inflows

£51,000

Base + Bonus + Overtime

Assessable Gross Income

£48,000

£923.08 / week

Statutory Rate Band

Basic Plus Rate

Exceeds £800/wk threshold

Annual Cap Headroom

£108,000

Until £156k Statutory Ceiling

Income Stream Inflows & Deductions

What Is Included and What Is Deducted from Gross Income

Income Breakdown

Mandatory Assessable Inflows

• Basic Gross Contractual Salary
• Guaranteed & Discretionary Bonuses
• Overtime, Shift Allowances & Commission
• Taxable P11D Benefits (Company Cars, Fuel)

Statutory Allowable Deductions

• 100% of Employee Pension Contributions
• Personal SIPP Contributions
• Household Dependent Children Discount (11–16%)
• Statutory Redundancy Pay (up to £30k tax-free)

Defining Gross Assessable Income Under the 2012 Scheme

The 2012 statutory child maintenance scheme uses gross taxable income as its baseline. Unlike take-home net pay, gross income is calculated before the deduction of income tax and employee National Insurance contributions.

The CMS accesses this information directly from HMRC through the Real-Time Information (RTI) system. When an employer files monthly payroll, the taxable gross pay figure is automatically captured for the annual review.

RTI Taxable Pay Feeds: Bonuses, Commission & Overtime

Any performance bonus, commission check, or overtime pay that is subject to income tax counts as gross income. If you receive an irregular bonus in March, HMRC reports the spike to the CMS, which can increase the assessment if an annual review occurs or if a parent requests a reassessment.

Mid-Year Pay Changes & the 25% Fluctuation Rule

Under Regulation 34, the CMS will not alter an existing child maintenance calculation for minor pay rises or small overtime drops. An in-year recalculation will only occur if gross assessable earnings change by at least 25%.

Changes of less than 25% are reconciled at the scheduled 12-month Annual Review without generating backdated debt.

Legal Clarifications

Frequently Asked Questions: Child Maintenance Income Calculator

Authoritative answers based on current statutory rules and legal precedents

Is child maintenance calculated on gross or net pay? ↓

Under the CMS 2012 scheme, child maintenance is calculated strictly on GROSS taxable income (before income tax and National Insurance), not net take-home pay. Pension contributions and resident dependent children allowances are deducted from this gross figure.

Are overtime and annual performance bonuses included in gross income? ↓

Yes. Overtime, commissions, and performance bonuses reported to HMRC via Real-Time Information (RTI) are included in the annual gross figure used to establish weekly liability.

Which employer benefits in kind (P11D) count as income? ↓

Taxable benefits in kind listed on your P11D (such as company cars, private medical insurance, and fuel allowances) are included in your gross taxable income by HMRC and evaluated by the CMS.

What deductions are legally allowed from gross income? ↓

The primary allowable deductions are: 100% of registered employee pension contributions (workplace salary sacrifice or private schemes) and the statutory household discount for other dependent children living with the paying parent (11% for 1, 14% for 2, 16% for 3+).

How does redundancy pay affect child maintenance income? ↓

Statutory redundancy pay (up to £30,000 tax-free) is exempt from taxable income. However, contractual redundancy, pay in lieu of notice, and severance amounts subject to income tax are treated as taxable income.

What is the 25% change threshold for income reviews? ↓

Under Regulation 34, the CMS will only recalculate an assessment mid-year if a parent’s gross income changes by at least 25% (up or down). Changes under 25% wait until the scheduled annual review.

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