What this calculator does

Run this scenario in DocketMath using the Cms Child Maintenance calculator.

DocketMath’s CMS Child Maintenance calculator helps you estimate child maintenance under the UK Child Maintenance Service (CMS) rules for many typical situations. A key part of the calculation is how the paying parent’s pension income and pension payments are treated when working out assessable income.

Because CMS uses detailed rules about income, deductions, and benefits, pensions can affect the result in more than one way:

• Pension income (money the paying parent receives regularly) may be treated as part of assessable income.
• Tax relief / adjustments can affect what counts as “income” for calculation purposes.
• Employer pensions vs. personal pensions can matter depending on how they’re paid and what documentation you have.
• Lump sums and irregular payments may be treated differently than regular pension income.
• Some situations involve additional deductions (for example, certain benefit offsets or allowances), and pensions can interact with these.

If you’re trying to understand “why did my number go up or down?”, the pension section is often the reason—especially where the paying parent receives a workplace pension or a state pension.

Typical pension-related inputs the calculator can reflect

Depending on what you enter, you may be asked for:

• Net regular pension income (or an amount CMS would effectively treat as income)
• Whether the pension is ongoing versus one-off
• Estimated weekly/monthly amounts (the calculator expects values aligned to its calculation method)
• Any other income components you include (because pensions are rarely the only figure)

To start using the tool directly, go here: /tools/cms-child-maintenance.

When to use it

Use the DocketMath calculator when you want to model child maintenance before you submit information to CMS—or when you’re reviewing how a change might affect the ongoing assessment.

Here are common triggers:

You should consider pension impact if…

• The paying parent starts claiming a new pension (e.g., a workplace pension begins at a specific age).
• The paying parent’s pension amount changes (annual increases, indexation, early retirement options).
• A pension payment switches from lump sum to regular instalments.
• One parent receives state pension and you want to understand how that affects maintenance.
• There’s been a change in household circumstances (for example, a new partner, additional children, or a different care pattern), and you suspect pensions are now relevant in the overall income picture.

You may need caution if…

• You only know your pension amount roughly. CMS-style calculations often expect consistent, evidence-backed figures.
• The pension payments are irregular (ad hoc withdrawals, variable annuities, or one-off settlements).
• The pension includes components that are hard to classify (e.g., mixed benefits, commuted sums, or payments with special rules).

Step-by-step example

Below is a practical walk-through showing how pensions can change the output. The numbers are illustrative to demonstrate mechanics, not a guarantee of any official CMS figure.

Scenario

• Paying parent has one child
• Child lives primarily with the receiving parent
• Paying parent receives:

  • State pension: £1,050 per month (net equivalent for modeling)
  • Workplace pension: £450 per month (net equivalent for modeling)
• No other major income changes are included in this example

Step 1: Choose your base inputs

Open the tool: /tools/cms-child-maintenance.

Then enter the key items the calculator requires (examples below—match the tool’s fields exactly):

• Number of children: 1
• Child arrangement / care pattern: enter the option that corresponds to your situation
• Paying parent income fields: include pension figures where the calculator asks for them

Step 2: Enter the pension figures

In the pension-related section, enter:

• State pension amount: £1,050/month
• Workplace pension amount: £450/month

If the calculator asks for weekly values instead of monthly, convert consistently. For quick conversion:

• Monthly to weekly ≈ monthly ÷ 4.345

So:

• State pension weekly ≈ 1,050 ÷ 4.345 ≈ £242/week
• Workplace pension weekly ≈ 450 ÷ 4.345 ≈ £104/week

Total pension weekly ≈ £346/week

Step 3: Review how the calculator totals income

The tool will combine your pension income with any other income you entered (if applicable). That combined figure is then used to compute the weekly maintenance estimate.

A simplified way to think about the impact:

• Higher assessable income from pension → potentially higher maintenance
• Missing pension income entirely → likely underestimation

Step 4: Observe the output

At the end, you’ll get an estimated maintenance amount. The most useful part for decision-making is often not just the final number, but how sensitive it is to pension changes.

Quick comparison: pension changes and output movement

Below is a small “what-if” comparison to show how pensions can drive the result.

Common scenarios

Pension effects are not one-size-fits-all. These are the scenarios that most often produce different outcomes when pensions are involved.

1) State pension increases after revaluation

If the paying parent receives the state pension and it increases (common each year in line with government uprating rules), then:

• A higher regular pension income can raise the assessable income used in the calculation.
• Your estimate should be updated at the time the increase takes effect.

What to do in the tool:

• Update the pension amount to the current monthly/weekly figure you’re using for modeling.

2) Workplace pension starts part-way through the year

A workplace pension may begin on a specific start date. That means:

• For estimates, CMS-style calculations often use the amounts relevant to the assessment period.
• If you’re modeling “now,” use the current regular amount rather than your past income.

What to do in the tool:

• Enter the pension as ongoing if it’s already in payment.
• If it starts later, consider modelling the new payment amount separately so you can compare scenarios.

3) Lump sum commutation or one-off pension withdrawal

This is where people commonly go wrong. A lump sum may not function like regular income.

Common pitfall patterns:

• Spreading a lump sum across 12 months as if it were regular pension income.
• Entering it as monthly pension payments without evidence it’s paid on an ongoing basis.

What to do in the tool:

• Use the pension income fields for regular payments.
• If the tool doesn’t support lump sums as a separate category, keep your lump-sum assumptions out of the pension income field and model only regular pension payments.

4) Pension that is paid in a variable way

Some pension arrangements pay irregular amounts or variable income. Examples include certain annuities or employer arrangements with varying payments.

What to do in the tool:

• Use the most consistent “typical” ongoing figure you can justify for modeling purposes.
• Document the basis of your estimate (e.g., last 3 months average) so you can update it when the pension history changes.

5) Deductions and income classification questions

The calculator’s treatment depends on how it expects your inputs to be categorized. If you enter pension figures in the wrong income type (income vs. deduction), the output can change.

Checklist to avoid mis-entry:

• Pension amounts entered should reflect regular net/estimated figures according to the calculator’s instructions.
• Only add other adjustments you’re confident the tool supports (and that you can evidence).

Tips for accuracy

A good estimate depends on accurate pension inputs and a careful approach to how amounts are entered.

Use consistent time periods

CMS calculations are typically framed around weekly amounts. If the tool accepts monthly amounts, use the tool’s intended format.

Best practice checklist:

• Enter pension amounts in the unit the tool asks for (weekly or monthly)
• If converting, apply the same conversion logic across all pension components
• Recheck decimals (rounding can affect totals)

Separate regular pension payments from irregular events

If your pension includes both regular payments and occasional adjustments:

• Model the regular portion in the pension income field
• Treat one-offs separately—either outside the pension income entry or by running a separate scenario if the tool can capture it

Keep evidence-ready notes

Even though you’re estimating, your inputs should be evidence-compatible.

Create a short “pension evidence” note in your records:

• State pension: current monthly/weekly amount
• Workplace pension: current monthly/weekly amount
• Payment dates (optional but helpful)
• Any scheduled increase dates

Run “change scenarios” before you decide what to do next

Because pensions can change, you’ll often get more value by comparing scenarios than by chasing a single figure.

Here are three scenarios worth trying in the tool:

• Current pension amounts
• Pension after a planned increase
• Pension with one component removed (to see the sensitivity)

Watch for classification issues

Different pension types can be treated differently depending on what they actually pay out and

Related reading

• Spreadsheet checks before running interest in United Kingdom — Spreadsheet validation before import
• How to interpret interest results in United Kingdom — What each output means and what moves the result
• Choosing the right interest tool for United Kingdom — How to choose the right calculator