What this calculator does

DocketMath’s CMS Child Maintenance Calculator (Northern Ireland) helps you estimate child maintenance payments under the Child Maintenance Service (CMS) rules that apply in Northern Ireland.

In plain terms, it takes key facts you provide about the child(ren) and the parents’ circumstances and then produces:

• an estimated weekly payment (or range, depending on the inputs)
• a clear breakdown of the inputs that drive the result (for example, number of children and income assumptions, plus how shared care affects the outcome)

This guide is designed to help you understand the calculator’s logic and how to interpret its outputs—without replacing the CMS assessment process.

What the calculator is built around

CMS calculations generally rely on:

• the number of children and how many are expected to live with each parent
• each parent’s income
• any shared care arrangement (sometimes described as “overnight stays” or similar patterns)
• the effective start date for the estimate (so rules can be aligned to the relevant period)

The DocketMath tool focuses on the inputs you can reasonably provide. If your real-world circumstances include complexities (non-standard expenses, special educational needs, or irregular income), your actual CMS outcome may differ.

Output you can expect

Typically, you’ll see outputs like:

• weekly child maintenance
• potential changes when you update income figures or alter the number of children
• an implied sensitivity: if you adjust one input (e.g., income or shared care), you should see the estimate move

For best results, treat the calculator like a scenario simulator:

• “What if my income is £X?”
• “What if the care pattern changes?”
• “What if there are two children rather than one?”

If you want to run it now, use the tool here: /tools/cms-child-maintenance.

When to use it

Use DocketMath’s CMS Child Maintenance Calculator Northern Ireland when you want a realistic estimate for planning or discussion with the other parent.

Good times to run the calculator

Consider using it when you’re:

• setting up a new agreement or preparing for a CMS application
• reviewing how maintenance might change after a job change, promotion, or reduced hours
• updating after a life event such as:

  • a new child is born (or added to the claim)
  • a child leaving full-time education
  • changes to shared care patterns
• trying to understand how different income assumptions affect the payment level

Before you rely on the numbers

Before treating an output as “the amount,” check:

• you selected the correct jurisdiction and the matching situation for Northern Ireland
• the child count matches your situation (including whether the calculator covers all children included in the case)
• the shared care input reflects the typical pattern, not one-off weeks

Step-by-step example

Below is a worked example that shows how the result changes when you adjust inputs. The numbers are illustrative to demonstrate calculator behaviour.

Example scenario (one parent is the calculator user)

Facts you enter

Assume:

• Jurisdiction: Northern Ireland
• Parent A’s income (entered in the tool): £30,000/year
• Parent B’s income (entered in the tool): £18,000/year
• Number of children: 1
• Shared care: no regular shared care nights (so the calculator treats care as primarily with Parent A)
• Estimate start date: today (the tool may align this with the calculation period you choose)

Step-by-step through DocketMath

1. Open the tool

   • Go to: **/tools/cms-child-maintenance

2. Select the case basics

   • Choose Northern Ireland (if the tool confirms it or if you’re directed through a NI-specific flow)
   • Enter the number of children

3. Add each parent’s income

   • Enter Parent A’s income as the tool requests (for example, annual income).
   • Enter Parent B’s income similarly.
   • If you’re unsure whether your figure should be gross or net, follow the calculator’s label precisely. The tool’s fields are designed to match CMS-style income inputs.

4. Set shared care

   • If the child mostly lives with Parent A, choose the setting that reflects no regular shared care.
   • If you have an alternating pattern, use the shared care option that matches your typical week (not a one-off holiday).

5. Run the estimate

   • Review the displayed weekly payment estimate and any breakdown the tool provides.

What you should notice

In this example:

• the payment is based primarily on the income gap
• with 1 child and no shared care, the weekly amount is typically higher than if shared care were entered

Even if the tool shows a single number, mentally compare it to two “what if” variants:

• If a second child is added: the weekly estimate generally increases.
• If shared care increases: the weekly amount often decreases (because the child spends significant time with both parents).

Second mini-example: same incomes, but shared care changes

Keep:

• Parent A: £30,000/year
• Parent B: £18,000/year
• Children: 1

Change:

• Shared care: enter a regular shared care arrangement

Result effect you should expect:

• DocketMath’s estimate should shift downward relative to the no-shared-care result
• the tool may show a different weekly amount based on the shared care setting you selected

Common scenarios

Below are realistic situations people enter into CMS calculators in Northern Ireland, and how each one tends to affect the estimate in DocketMath.

Scenario checklist

Use these as quick prompts for your own inputs:

Typical scenario patterns

1) One child, full-time with Parent A

• Expect a baseline estimate driven by the income difference
• Shared care set to “none” tends to produce the higher estimate

2) Two children, similar incomes to scenario 1

• The weekly total often increases because the calculation considers the number of children

3) Shared care enters the picture

• As shared care increases, the weekly obligation often decreases
• DocketMath’s output should respond when you:

  • change shared care options
  • adjust any shared care details the tool uses (for example, overnight stay logic)

4) Income differs due to employment change

• If Parent A moves from £20,000/year to £28,000/year, your estimate should increase
• If Parent B’s income drops or rises, the payment estimate adjusts accordingly

5) Parent income is difficult to pin down

You may still be able to use the calculator in a “range” style:

• run with a lower plausible income
• run again with a higher plausible income
• compare the output difference to understand sensitivity

This helps you plan conversations and budgets while you gather documentation.

Tips for accuracy

Small input differences can create big output swings. These tips focus on using DocketMath’s fields in the most reliable way.

Income inputs: get the field-to-number mapping right

Practical example: avoiding a common mismatch

If one parent’s income is entered as “gross annual salary,” but the other is accidentally entered as “take-home pay,” the estimate will likely be distorted. The calculator’s output can only be as accurate as your inputs.

Shared care: enter the true pattern

Children: count correctly

Dates: align to the period you’re estimating

If the calculator asks for an estimate start date or calculation period:

• choose the date that matches when you want the estimate to apply
• use the same date across multiple scenario runs so comparisons remain fair

Use the tool for comparisons, not only single-point answers

Try this workflow:

• Run 1: baseline (current situation)
• Run 2: income increase/decrease for one parent
• Run 3: shared care change (more or fewer regular nights)
• Run 4

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