Child Maintenance Calculator
The official CMS calculator uses gross income, which most people don't know off the top of their head. Ours uses your net take-home pay, so you instantly see what you'd actually pay or receive.
Still called a CSA calculator by most people, and child support by some. Same rules, same 2026/27 rates, for England, Wales, Scotland and Northern Ireland.
Child Maintenance Calculator
Enter your gross salary. We work out the tax, the NI and your CMS amount
Your salary before tax and NI are deducted, shown on your payslip as "Gross Pay".
Enter the same period as above (e.g. monthly if you selected "per month"). Salary sacrifice only. These are deducted before tax and reduce what the CMS counts as your income. Personal pension payments outside of payroll do not reduce CMS income.
What counts as an overnight stay? (important, read this)
Under Schedule 1, paragraph 7 of the Child Support Act 1991 and Regulation 46 of the Child Support Maintenance Calculation Regulations 2012, a night only counts if:
The child physically sleeps overnight at the paying parent's address.
The CMS counts the total expected nights per 12-month period from the effective date. It will ask for evidence: a court order, agreed schedule, or established pattern.
DOES count
- ✓Child sleeps at the paying parent's home overnight
- ✓Nights during school holidays where the child stays over
- ✓Regular weekly overnight contact (e.g. every other weekend)
- ✓Overnight stays ordered by a court (court order is strong evidence)
- ✓Hospital stays where the paying parent would normally have the child that night
Does NOT count
- ✗Daytime visits, however long, even full days
- ✗Picking up and dropping off without an overnight stay
- ✗Nights the child spends at grandparents' or other relatives
- ✗Staying at a friend's house arranged by the paying parent
- ✗Nights where the child is not at the paying parent's address
How nights reduce your payment (Schedule 1, para. 7, CSA 1991)
| Nights per year | Reduction | What this means |
|---|---|---|
| 0–51 | None | No reduction applied |
| 52–103 | 1/7 deducted | ~1 night/week on average |
| 104–155 | 2/7 deducted | ~2 nights/week on average |
| 156–174 | 3/7 deducted, minus £7/wk | ~3 nights/week on average |
| 175+ | 1/2 deducted, minus £7/wk | Roughly equal care |
If nights are shared across multiple children in the same household, the fractions are averaged. At 156+ nights an additional £7/week is subtracted per qualifying child. If this would reduce the payment below £7/week, the minimum payable is £7/week.
View Regulation 46 (2012 SI) on legislation.gov.ukIf the paying parent has other children living with them (not related to this case), their gross income is reduced before the CMS calculation. This applies to children they live with full-time or share care of.
Some situations override the standard calculation and result in a flat rate or nil rate.
Based on UK CMS rates and HMRC 2026/27 tax thresholds. For guidance only, not legal advice.
How the CMS works out your payment
The Child Maintenance Service does not weigh up what a child costs, what you can afford, or what either household needs. It runs a formula. Understanding the formula is the difference between accepting a figure and knowing whether it is right.
The calculation is set out in the Child Support Maintenance Calculation Regulations 2012. It runs in six steps, and the CMS applies them in this order every time.
- Take gross annual income from HMRC. Not your payslip, not what you tell them. The CMS pulls the figure straight from HMRC records for the most recent complete tax year it holds.
- Deduct pension contributions. Occupational and salary sacrifice contributions are already out of the HMRC figure. Personal pension contributions are not, and the CMS will only remove them if you tell it about them.
- Apply a reduction for other children living with you. 11% off for one, 14% for two, 16% for three or more. This happens before the main percentage, so it compounds.
- Convert to a gross weekly figure and pick a rate band. Nil, flat, reduced, basic or basic plus, depending on where the weekly figure lands.
- Apply the percentage for the number of qualifying children. 12%, 16% or 19% on the basic rate.
- Reduce for shared care. Counted in overnight stays per year, in four bands.
The five income bands
Most people assume the 12/16/19 percentages always apply. They only apply in the basic band, which covers gross weekly income from £200 to £800. Above and below that, the rules change.
| Rate | Gross weekly income | What you pay |
|---|---|---|
| Nil | Under £7, or on certain benefits as a student or prisoner | Nothing |
| Flat | £7 to £100, or receiving most benefits | £7 a week regardless of the number of children |
| Reduced | £100.01 to £199.99 | £7 plus a percentage of income above £100 |
| Basic | £200 to £800 | 12% for 1 child, 16% for 2, 19% for 3 or more |
| Basic plus | £800.01 to £3,000 | Basic rate on the first £800, then 9% / 12% / 15% on the rest |
Gross weekly income above £3,000, which is £156,000 a year, is ignored entirely. If the paying parent earns more than that, the receiving parent has to go to court for a top-up order under section 8 of the Child Support Act 1991. The CMS cannot help.
How much child maintenance for 1 child, 2 children or 3 children
This is the question almost everyone arrives with, and the honest answer is that there is no single amount. The figure depends entirely on the paying parent's gross income. What is fixed is the percentage, and the table below turns that into pounds at the salaries most people are actually on. It assumes no shared care, no other children in the household and no pension contributions, so these are the maximum figures before any reductions.
| Gross salary | Gross weekly | 1 child | 2 children | 3+ children |
|---|---|---|---|---|
| £25,000 | £480.77 | £57.69 | £76.92 | £91.35 |
| £30,000 | £576.92 | £69.23 | £92.31 | £109.62 |
| £35,000 | £673.08 | £80.77 | £107.69 | £127.88 |
| £40,000 | £769.23 | £92.31 | £123.08 | £146.15 |
| £45,000 | £865.38 | £101.88 | £135.85 | £161.81 |
| £50,000 | £961.54 | £110.54 | £147.38 | £176.23 |
| £60,000 | £1,153.85 | £127.85 | £170.46 | £205.08 |
All the figures above are weekly, because that is how the regulations are written. To get a monthly figure, multiply by 52 and divide by 12. One child on a £30,000 salary is £69.23 a week, which is £300 a month. The CMS bills monthly but calculates weekly, and the rounding is where a lot of confusion starts.
Two children is not double one child. Three is not triple. The percentage covers the whole case rather than being charged per child, so the second child adds 4% of income and the third adds 3%. A fourth adds nothing at all.
Notice what happens between £45,000 and £60,000. The salary rises by a third but the maintenance rises by a quarter, because everything above £800 a week is charged at the lower basic plus rates.
Why gross income makes the figure feel wrong
On £45,000 the CMS assesses you on £865.38 a week. Your actual take-home is closer to £670 a week once income tax and National Insurance come out. The percentage is applied to money you never see.
For one child, £101.88 a week is 11.8% of your gross pay but 15.2% of what actually lands in your account. That gap is the single most common reason paying parents believe the calculation is broken. It is not an error. It is how the regulations are written, and no amount of arguing with a caseworker will change it.
This calculator exists because of that gap. Enter what you take home and you can see both numbers side by side. If you want to see what the payment would look like if the CMS deducted rent and bills first, our living costs calculator models that. It is hypothetical. The CMS does not work that way and will not accept it.
Shared care: the four bands
Overnight stays are the largest single lever most paying parents have. The CMS counts nights, not days, not hours, and not how involved you are. A full day every weekend with no overnight stay reduces your payment by nothing at all.
| Nights per year | Roughly | Reduction |
|---|---|---|
| 52 to 103 | 1 night a week | One seventh |
| 104 to 155 | 2 nights a week | Two sevenths |
| 156 to 174 | 3 nights a week | Three sevenths |
| 175 or more | Roughly half the year | Half, then another £7 a week off |
The band boundaries are sharp. Going from 51 nights to 52 nights cuts a £100 a week payment by £14.29 a week, which is £743 a year, for one extra night. Going from 103 to 104 does the same again. If your arrangement sits just under a boundary, it is worth counting carefully.
What reduces the figure, and what does not
These genuinely reduce your assessment:
- Pension contributions, including personal pensions if you report them
- Other children living in your household, at 11%, 14% or 16% off your income
- Shared care nights, in the four bands above
- A successful variation for special expenses, such as long-distance contact travel costs
These change nothing:
- Your rent, mortgage, bills or debts
- Your new partner's income
- Buying clothes, school trips, birthdays or holidays for the child
- Daytime contact, however frequent
- The receiving parent's income, which is completely irrelevant to the calculation
What this calculator cannot know
It cannot see the HMRC figure the CMS is actually using, and that is the most common source of a mismatch. HMRC data lags. If you are self-employed it can be 12 to 18 months behind, because it comes from a Self Assessment return covering a tax year that has already ended.
It also cannot model a variation, a company director's dividends, or a case where the CMS has applied a default assessment because it has no income data at all. If any of those apply, start with the self-employed guide or the company director guide.
If your figure looks wrong and you want it changed, the route is a mandatory reconsideration within one calendar month of the decision. Our letter generator builds one and works out your deadline.
Common questions
How much child maintenance will I pay on £30,000 a year?
£30,000 gross is £576.92 a week. On the basic rate that is 12% for one child (£69 a week), 16% for two (£92 a week) and 19% for three or more (£110 a week). Shared care nights, pension contributions and other children living with you all reduce these figures.
How much child maintenance should I pay for 1 child?
On the basic rate it is 12% of your gross weekly income. On £30,000 a year that is £69.23 a week, or £300 a month. On £45,000 it is £101.88 a week, because everything above £800 a week is charged at 9% rather than 12%. Shared care nights and other children in your household bring both figures down.
How much child maintenance is paid for 2 children?
16% of gross weekly income on the basic rate, and 19% for three or more. Two children on a £30,000 salary works out at £92.31 a week. It is not double the one-child figure, because the percentage covers all the children in the case rather than being charged per child.
What percentage is child maintenance in the UK?
12% for one child, 16% for two and 19% for three or more, applied to gross weekly income between £200 and £800. Between £800 and £3,000 a week the rate drops to 9%, 12% and 15% on the portion above £800. Below £200 a week there are flat and reduced rates instead, and nothing at all is charged above £3,000 a week.
Is this the same as a CSA calculator?
In practice, yes. The CSA closed in 2012 and the Child Maintenance Service replaced it, but most people still search for a CSA calculator out of habit. Every live case now runs on the CMS rules this calculator uses. The only reason the old CSA rules still matter is historic arrears, which never expire.
Does this calculator work in Scotland and Northern Ireland?
In Scotland and Wales, yes, without any adjustment. Child maintenance is reserved to Westminster, so the formula, the percentages and the shared care bands are identical. Northern Ireland runs a separate Child Maintenance Service under its own legislation, but the calculation rules mirror Great Britain, so the figure this tool produces still holds. Scottish income tax rates differ, so the net to gross step is an approximation north of the border.
Does the CMS use gross or net income?
Gross. The CMS takes your gross annual income directly from HMRC, before income tax and National Insurance are deducted. This is why the figure feels high compared to what you actually take home, and it is why this calculator lets you work backwards from your net pay.
Why is the CMS figure different from my own calculation?
The most common reasons are that the CMS is using an HMRC income figure from a previous tax year, that pension contributions have or have not been deducted, or that the number of shared care nights it holds does not match reality. All three are challengeable.
Is there a maximum amount of child maintenance?
Yes. The CMS only applies its percentages to gross weekly income up to £3,000, which is £156,000 a year. Above that the receiving parent has to apply to the courts for a top-up order. Income below £7 a week attracts no payment at all.
Does the calculator include pension contributions?
Yes. Enter your pension contributions and they are removed before the CMS percentage is applied, which is how the real calculation works. Occupational and salary sacrifice schemes reduce the figure HMRC reports automatically. Personal pensions do not, so you have to tell the CMS about those yourself.
Is this the official CMS calculator?
No. This is an independent tool. It applies the same rates and rules set out in the Child Support Maintenance Calculation Regulations 2012, but the CMS will use the exact HMRC figure for your case. Treat the result as an accurate estimate, not a decision.