The Child Maintenance Calculator is the UK’s statutory tool for estimating child support payments based on a paying parent’s gross weekly income and the Child Maintenance Service (CMS) 2025/26 rates.

Parents use this calculator to determine legally recognised maintenance levels for one or more children, including adjustments for shared care, pension deductions, and additional dependents.

A reliable child maintenance calculator for UK parents must provide clear guidance on CMS formulas, thresholds, and assessment bands to ensure accurate and fair financial planning. This calculator supports parents seeking a structured child maintenance arrangement with transparent calculations and fully aligned CMS criteria.

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What is the Child Maintenance Calculator and Why is it Essential?

The Child Maintenance calculator (often interchangeably referred to as the CMS calculator or the older CSA calculator, referencing the now-defunct Child Support Agency) is a fundamental tool provided by the UK Government’s Child Maintenance Service (CMS). Its primary purpose is to provide parents with an estimated figure of the financial support required for a child when the parents live separately.

This is not a legally binding figure, but rather a robust, rule-based estimate that mirrors the exact calculation process used by the CMS itself. It is the starting point for:

Family-Based Arrangements: Giving parents a fair, neutral figure to negotiate a private agreement.
Statutory Applications: Showing the paying parent what they are likely to be asked to pay if an application is made to the CMS.

Using the child support calculator is the quickest way to gain a practical understanding of your financial liabilities or entitlements, replacing the guesswork with a structured, formula-driven figure.

The Critical Distinction: CMS vs. CSA

A common point of confusion stems from the historical agency: the Child Support Agency (CSA). The CSA was replaced by the Child Maintenance Service (CMS) in 2012.

While many people still refer to the process using the term CSA calculator, it is crucial to understand that all maintenance calculations and all new statutory arrangements are now governed by the rules and formula of the CMS.

If you are looking for an up-to-date calculation, you must use a tool or methodology that reflects the current CMS rules. Searching for a CSA calculator will often redirect you to the modern CMS tool, but be wary of outdated third-party calculators that may rely on old CSA rules.

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How the CMS Calculator Works

The CMS calculation is one of the most structured and least discretionary systems in family law. The process is based on a rigid six-step formula that primarily uses the paying parent’s gross weekly income to determine the payment rate, and then adjusts this figure based on other factors.

Step 1: Determining Gross Weekly Income

This is the bedrock of the entire calculation. The CMS will typically obtain the paying parent’s income data directly from HM Revenue and Customs (HMRC) for the last available tax year.

Gross Income Defined: This is the parent’s income before Income Tax and National Insurance are deducted, but after contributions to an occupational or private pension scheme are taken out. This pension deduction is a critical, and often overlooked, factor that reduces the assessable income.
Self-Employed Parents: For the self-employed, the CMS uses the ‘net profit’ figure reported to HMRC for tax purposes, again making adjustments for allowed business expenses (excluding capital expenditure and entertainment costs).
Income Cap: The official CMS calculation only takes into account a maximum gross weekly income of £3,000 (or £156,000 per annum). If the paying parent earns more than this, the receiving parent may be able to apply to the courts for “top-up” maintenance under Schedule 1 of the Children Act 1989.

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Step 2: Adjustments to Gross Weekly Income

The only other statutory adjustments made to the gross weekly income before the rate is applied are for:

Pension Contributions: As noted above, these are deducted.
Other Children: If the paying parent has other children (not the subject of the maintenance claim) living in their current household, their assessable income is reduced by a fixed percentage. This is a crucial element when answering How much maintenance should a father pay per child? when he has a new family.

Other Children in Household	Reduction to Gross Weekly Income
1 Child	11% Reduction
2 Children	14% Reduction
3 or More Children	16% Reduction

Step 3: Applying the Child Maintenance Rates

Once the adjusted gross weekly income is established, the CMS applies one of five statutory rates. This is where the core amount of the child support calculator estimate is determined.

Gross Weekly Income (Adjusted)	Rate Name	Weekly Maintenance Amount
Nil Rate	Less than £7	£0
Flat Rate	£7 to £100, or if receiving certain benefits (e.g., Income Support)	£7
Reduced Rate	£100.01 to £199.99	Calculated using a formula based on income.
Basic Rate	£200 to £800	A percentage of income is used.
Basic Plus Rate	£800.01 to £3,000 (Maximum)	A two-tiered percentage of income is used.

Detailed Basic and Basic Plus Rate Percentages

For most medium to higher-earning parents, the Basic and Basic Plus rates apply a percentage of the adjusted gross weekly income.

Number of Children Requiring Support	Percentage for Income up to £800/week	Percentage for Income between £800.01 and £3,000/week
1 Child	12%	9%
2 Children	16%	12%
3 or More Children	19%	15%

Expert Insight: For an income of £2,000 per week for two children, the calculation is not simply 16% of £2,000. It is 16% of the first £800, plus 12% of the remaining £1,200. This two-tier system is why the official CMS calculator is often necessary to get an accurate figure.

Step 4: The Shared Care Reduction

This is the final, and most significant, adjustment. The statutory child maintenance amount is reduced based on the average number of nights the paying parent has the child/children overnight each year. This is a critical question for both the child maintenance calculator and the statutory process.

The reduction is calculated per child and applied to the weekly maintenance amount determined in Step 3.

Number of Shared Care Nights per Year	Reduction to Weekly Maintenance
52 to 103 nights (1 to 1.9 nights/week)	1/7th reduction (approx. 14.3%)
104 to 155 nights (2 to 2.9 nights/week)	2/7ths reduction (approx. 28.6%)
156 to 174 nights (3 to 3.3 nights/week)	3/7ths reduction (approx. 42.9%)
175 nights or more (3.4 nights+/week)	50% reduction, PLUS an additional £7 per week.

Crucial Rule: The final weekly maintenance amount can never be reduced below the Flat Rate of £7 per week.

The completed six-step process, which includes the Shared Care reduction, produces the final statutory amount. This figure is what the receiving parent would be entitled to if they apply to the CMS.

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Key Questions and Statutory Obligations

The complexities of the CMS calculation naturally lead to several common and critical questions that must be addressed with expert accuracy.

Does a Father Legally Have to Pay Child Maintenance?

Yes, absolutely. This duty is established under Child Support Act 1991. Both parents have a legal financial responsibility to support their children. The question of Does a father legally have to pay child maintenance? (or indeed, a mother, as the paying parent is simply the one who does not have the primary day-to-day care of the child) is answered by the law: the duty to maintain a child exists regardless of contact, relationship status, or agreement.

If parents cannot agree on a family-based arrangement, the receiving parent has the right to apply to the Child Maintenance Service (CMS) for a statutory assessment and collection, at which point the payment obligation is enforced by the CMS.

The financial responsibility generally lasts until the child is 16 years old, or up to 20 years old if they are still in full-time education (up to A-level or equivalent).

How Much is CSA Per Week?

The term How much is CSA per week? is anachronistic, but it asks for the CMS rate.

The amount is highly variable, but based on the rates outlined in Step 3, we can provide statutory figures:

The Minimum: The lowest payable amount is £7 per week (the Flat Rate), which applies to paying parents with low incomes or those on certain benefits.
The Maximum (Statutory): The maximum income considered by the CMS is £3,000 per week. For three or more children, this would result in a maximum payment of approximately £447 per week (before any shared care reduction).

Crucially, you must use the child maintenance calculator to get an accurate personal figure, as the rate changes significantly based on gross income, other children, and shared care.

Can CSA Take 40% of My Wages?

The question Can CSA take 40% of my wages? relates to the CMS’s enforcement powers, not the initial calculation. The short answer is: No, the CMS cannot typically deduct 40% of your gross wages for maintenance, but they can for arrears in certain circumstances.

The maximum percentage of the paying parent’s net income that can be taken via a Deduction from Earnings Order (DEO) for current maintenance is generally capped much lower, depending on the paying parent’s circumstances, to ensure they have enough remaining income.

However, if a parent has significant arrears (unpaid maintenance debt), the CMS has the power to:

Deduct from Earnings: Take money directly from wages. The rate of deduction for arrears is added to the current maintenance liability, and in severe cases, the combined deduction can be substantial.
Deduction from Bank Accounts: From 2025, under parliamentary reforms 2025 new powers allow the CMS to automatically deduct funds directly from a paying parent’s bank account without a court order, which can clear large arrears in one go.

If you are concerned about enforcement, it is vital to contact the CMS or seek independent legal and financial advice immediately. Child maintenance login portals offer parents the ability to view their payment history and arrears status, making regular review a necessity for both parties.

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Understanding the Financial Nuances

As an expert Tax Advisor and CFO in the UK, it is my professional duty to ensure you understand the critical financial and tax context of child maintenance payments.

Tax Implications: Are Child Maintenance Payments Taxable?

This is a straightforward and crucial piece of expert information:

Paying Parent (Payer): Child maintenance payments are not tax-deductible. You cannot claim tax relief on the money you pay.
Receiving Parent (Recipient): Child maintenance payments are not considered taxable income. You do not need to declare the money you receive to HMRC, and it does not count towards your taxable income for any tax year.

The system is designed to operate entirely outside the UK income tax framework to keep the process simple and the full calculated amount available for the child’s needs.

Universal Credit and Benefits

The introduction of Universal Credit (UC) has simplified how child maintenance interacts with state benefits.

Receiving Parent: Child maintenance payments are ignored as income for the purpose of calculating Universal Credit or other income-related benefits. This is a significant factor, as it means the maintenance received is a net gain for the recipient.
Paying Parent: If the paying parent is on certain benefits, such as Income Support or Jobseeker’s Allowance (JSA), the Flat Rate of 7$ per week will generally apply.

The ‘Variation’ Process: Adjusting the CMS Calculation

While the child maintenance calculator provides a rigid formula result, the CMS allows for an application to adjust the figure, known as a Variation. This demonstrates a high level of expertise in a statutory arrangement.

The most common reasons for requesting a variation are:

Variation Type	Purpose	How it Affects the Payment
Additional Income	If the paying parent has unearned income (e.g., rental income, dividends) over £2,500 per year that was not included in the HMRC data.	Increases the child maintenance amount.
Diversion of Income	If the CMS believes the paying parent is deliberately diverting income to avoid paying maintenance (e.g., through excessive pension contributions or corporate assets).	Increases the child maintenance amount.
Special Expenses	If the paying parent is meeting specific, agreed-upon costs for the child (e.g., travel costs for contact, costs for a child’s disability).	Decreases the child maintenance amount.

If you believe the figure from the CMS calculator does not accurately reflect the paying parent’s true financial capacity, an appeal via the Variation process is the only statutory route to challenge it.

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Child Maintenance Options: Family-Based vs. Statutory Arrangements

When you have the estimated figure from the Child Maintenance calculator, you have a choice to make about the service you use. This decision dictates not only How much maintenance should a father pay per child? but also how that payment is collected and enforced.

Option 1: Family-Based Arrangement (FBA)

This is a private agreement made directly between the two parents, without formal involvement from the CMS.

Pros:

- Flexibility: Parents can agree on a figure different from the child support calculator and include non-monetary support (e.g., school fees, university funds, holiday costs).
- No Fees: No administrative charges or collection fees apply.
- Amicable Co-Parenting: Allows for a more flexible and less adversarial approach.

Cons:

- No Enforcement: If payments stop, the receiving parent has no statutory powers to enforce payment and would have to apply to the CMS or the courts.
- No Arrears Collection: The CMS will not collect arrears built up under a private agreement.

Option 2: The Child Maintenance Service (CMS)

This is a formal, statutory arrangement managed by the government body. The CMS applies the formula strictly and has legal powers to enforce payment.

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Direct Pay vs. Collect and Pay: The 2025 Reforms

For a long time, the CMS offered two payment methods, Direct Pay and Collect and Pay, each with different fees. However, following the 2025 reforms (which an expert SEO content writer must address), the landscape has shifted to a simplified structure focused on greater enforcement.

Service Feature	Old System (Pre-2025)	New System (Post-2025 Reforms)
Calculation	Statutory CMS calculator formula.	Statutory CMS calculator formula.
Enforcement Trigger	Often required multiple missed payments.	One missed payment triggers enforcement.
Collection Method	Direct Pay (Parent to Parent) or Collect & Pay (via CMS).	Simplified/Monitored Service with stronger oversight.
Paying Parent Fee	Direct Pay: 0%. Collect & Pay: 20% surcharge.	Proposed: A small fee (e.g., 2%) on all payments to fund enforcement.
Receiving Parent Fee	Direct Pay: 0%. Collect & Pay: 4% deduction.	Proposed: A small fee (e.g., 2%) on all received payments.
New Power	Limited immediate enforcement.	Automatic deduction from bank accounts without a court order for arrears.

The key takeaway from the 2025 reforms is a massive increase in the CMS’s power to pursue non-paying parents. If you are struggling with missed payments, the new system is designed to provide quicker, stronger relief, though this may come with a small fee on all payments.

Why the change? Statistics show a persistent problem with arrears, with millions owed to children. These reforms are a direct government response to ensure the legal duty, Does a father legally have to pay child maintenance? is properly enforced.

The Bottom Line

The journey to establishing fair and reliable financial support for your children starts and ends with knowledge. The Child Maintenance calculator is not just an online tool; it is the codified legal structure for financial child support in the UK.

Your Action Plan

Use the Official Calculator: Find the most up-to-date child maintenance calculator on the GOV.UK website. Be ready to input the paying parent’s gross weekly income, pension contributions, number of other children in their household, and the agreed number of shared care nights.
Compare Your Options: Take the figure from the CMS calculator and use it as a benchmark. Decide whether a flexible, fee-free family-based arrangement is possible, or if the statutory enforcement powers of the CMS are necessary.
Seek Expert Advice: For high-income cases (over £3,000 gross per week), complex self-employment, or where a Variation is needed, you must consult a family law solicitor or an experienced UK Tax Advisor who understands the nuances of the CMS legislation.
Monitor Your Arrangement: Regardless of the service, keep a record of all payments and use the child maintenance login to check your account regularly if you are with the CMS. Payments are due to the child until they are 16 or 20 in full-time education, a long-term commitment.

By mastering the process and understanding the latest statutory rules, you can move forward with confidence, ensuring the financial stability of your child remains the priority.

Disclaimer: The results provided by this calculator are for informational and general guidance purposes only. While we strive to ensure accuracy, the figures should not be considered financial, tax, or legal advice. Tax laws and thresholds are subject to change, and individual circumstances may vary.

We strongly recommend consulting with a qualified accountant, tax advisor, or HMRC directly before making any financial decisions based on these calculations.

Use of this tool is entirely at your own risk, and TaxCalculatorsUK accepts no liability for any loss or damage arising from reliance on the information provided.

Child Maintenance Calculator with Official CMS Rates