What this calculator does

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

DocketMath’s CMS Child Maintenance Calculator (UK) helps you estimate child maintenance using the Child Maintenance Service (CMS) formula framework used in the UK. The output is a calculation estimate, not an official decision, and it can differ from the CMS if your case includes specific circumstances that require more detailed treatment than the baseline model.

At a glance, the calculator is designed to help you understand how key inputs typically affect the result, such as:

• Which income inputs usually matter (and how changes move the estimate up or down)
• How the number of children changes the estimate
• How percentage bands and set allowances influence the calculation
• What happens when you compare scenarios (for example, different incomes or different care patterns)

Because CMS rules can be updated and because assessments can depend on case-specific context, use the calculator as a planning and understanding tool rather than a substitute for an official CMS assessment.

If you want to run the calculation, you can use DocketMath’s tool here: /tools/cms-child-maintenance.

When to use it

Use DocketMath’s calculator when you want a quick, structured way to model maintenance before you:

• start a conversation with the other parent
• prepare for a CMS application or review
• sanity-check figures mentioned by someone else
• compare scenarios (for example, income changes or different numbers of children)

Common moments where a formula-based estimate can help:

• New agreement discussions: You have an approximate income figure and want to see what a realistic range might look like.
• Change in circumstances: Your pay has changed, you’ve started overtime, or there’s been a change to your benefits situation.
• More/less children involved: Additional children or different household arrangements can affect how maintenance is calculated.
• Budgeting: You need a monthly number to plan housing, childcare, and school costs.

Avoid using it as your only tool when your case involves complex factors. In those situations, you can still use the calculator as a baseline, but treat the output as directional and consider seeking tailored guidance.

Complex scenarios that may require deeper rule application

• Shared care / court-ordered arrangements where care percentages matter
• Non-cash benefits or mixed income streams
• High income levels where different rules and caps may apply
• Special expenses that CMS may consider separately from standard maintenance

Step-by-step example

Below is a worked example to show how the inputs map to the calculation conceptually. The exact internal steps depend on the calculator’s implementation and the chosen inputs, but the overall CMS-style structure is consistent: assess income → apply allowances → apply a percentage by income band → adjust for shared-care patterns → produce a monthly maintenance estimate.

Example: Two children, moderate income, no shared care

Assumptions for the example (for illustration):

• The paying parent earns £2,300/month net-equivalent for calculation purposes (enter the closest figure the calculator asks for)
• The receiving parent has 2 children
• There is no shared care pattern applied in the calculator
• No additional adjustments beyond the baseline model

Step-by-step through the calculator logic

1. **Choose the jurisdiction context (UK)

   • The calculator is built specifically for GB (United Kingdom).

2. Enter income

   • Put your estimated figure into the income field(s).
   • Keep everything in the same time unit (for example, don’t mix weekly and monthly figures).

3. Enter the number of children

   • Set 2 children.

4. Set shared care

   • If the calculator asks for a shared-care percentage or a shared-care toggle, choose the option that matches your situation.
   • For this example, choose no shared care.

5. Review the estimated assessable income

   • CMS-style models commonly treat the maintenance calculation as based on an assessable amount, not necessarily your raw total income.
   • Your assessable figure is typically derived after allowances and rule-based income treatment.

6. Apply the formula band

   • The calculator then applies a percentage rate associated with the income band where your assessable income falls.
   • Because bands step up at thresholds, the estimate can increase non-linearly across different income levels.

7. Multiply to get monthly maintenance

   • The model produces a monthly estimate (the presentation may align with CMS monthly amounts).

8. Check reasonableness

   • Compare the estimate against practical expectations:

     • whether the figure seems consistent with the paying parent’s income level you entered
     • whether the children count and shared-care selection match your real arrangement
     • whether you might have a unit mismatch (weekly vs monthly)

What you should notice in the example

• With 2 children, the calculator increases the overall figure compared to 1 child (depending on the bands and allowances).
• Shared care can be a major lever: even a small change in care input can affect the estimate meaningfully.
• Input units matter. A weekly/monthly mix-up can dramatically change the outcome.

Common scenarios

Below are scenario patterns you’ll likely run into. Use these to understand why your estimate changes when you tweak one input.

1) Income changes mid-year

Typical effect: maintenance estimates can rise or fall because the calculation uses income bands and percentage rates.

How to use the calculator:

• Run it using your current income.
• Run it again using your expected new income.
• Compare the difference to prepare for changes in monthly cashflow.

2) Adding or changing the number of children

Typical effect: moving from 1 child to 2 children usually increases the overall calculation because the children count affects the baseline.

How to use the calculator:

• Keep every other input constant.
• Change only the children count and observe the difference.

A useful way to interpret the output:

• If the estimate changes sharply, you may be near a threshold where bands step up.
• If the estimate changes modestly, you may be in an area where changes are smoother or where shared-care adjustments dominate.

3) Shared care (different attendance patterns)

Typical effect: shared care usually reduces the amount payable compared with a “no shared care” scenario, because the paying parent provides more direct care time.

How to use the calculator carefully:

• Choose the shared-care option that best matches your pattern.
• If your care arrangement fluctuates, focus on your overall pattern, not one exceptional week.

4) Partner income or household income confusion

In CMS-style formula calculations, the focus is typically on the paying parent’s income for the maintenance calculation, not a combined household income number.

How to use the calculator:

• Enter the income the calculator asks for in the correct field.
• Don’t average two households unless the calculator explicitly requires that.

If you’re unsure what income concept the tool expects, try one run with a conservative estimate to see whether the output feels plausible for your situation.

5) Benefits and special income types

Typical effect: different income types can be treated differently under CMS-style rules.

How to handle it in the calculator:

• Enter a figure that matches the calculator’s expected income input (for example, if it expects a net-equivalent monthly figure, use that).
• Avoid mixing gross and net pay in the same entry.

Quick comparison table (directional output relationships)

The table below shows directional relationships. Your exact amounts will vary depending on bands and allowances.

Tips for accuracy

Small input mistakes are one of the most common reasons estimates differ from official outcomes. Use this checklist before relying on the result.

Input accuracy checklist

How to sanity-check the output

Try these practical checks:

1. Does it fit your expectations?

   • If the estimate is far outside what you expected, revisit:

     • income units (weekly vs monthly)
     • shared care selection
     • children count

2. Use “what-if” runs

   • Increase income slightly (for example, by 5%).
   • Decrease income slightly (for example, by 5%).
   • If the estimate barely moves, you may be in a band region where small changes don’t trigger a threshold. If it jumps, you may have crossed a band.

3. Check shared-care sensitivity

   • Run once with “no shared care.”
   • Run again with a shared-care option that matches your arrangement.
   • If the estimate doesn’t change much, either shared care isn’t being applied the way you expect or the calculator’s shared-care input doesn’t match your circumstances.

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