How much is your child costing you?

Raising a child to the age of 18 will cost the average parents almost $250,000.

The calculation, included in a draft study for the Inland Revenue Department, covers only expenses. It doesn't count parents' loss of income or childcare costs.

The income lost by one parent staying at home during that period would be almost $165,000, based on the national average wage calculated by Statistics New Zealand - pushing the true total to almost a quarter of a million dollars.

The report, Costs of Raising Children, by Iris Claus, Geoff Leggett and Xin Wang, will be included in a Government review of the formula used to determine child-support payments.

It's the first time such figures have been calculated, with Revenue Minister Peter Dunne describing the findings as "stark".

The costs were defined as parental expenditures on children up to 18 years of age. They were determined by comparing two adult households with the same estimated standard of living - one with children and the other without.

The authors concluded that parents on a high income would spend almost three times as much on a single child as those on a low wage.

They also found costs for second and subsequent children could be reduced by the use of hand-me-downs - raising four children would cost parents on a middle income $686 a week

Not surprisingly, children aged 12 and under cost less than teens. But the figures covered only basic expenses, such as food, clothes and vital equipment.

Parenting guru Ian Grant, of Parents Inc, said parents did not have to spend a fortune to be good at it. Young children didn't know the difference between a designer cot and one bought from Trade Me.

Some parents were "over-the-top", possibly because they were older and better off than mothers and fathers from previous generations.

"You can spoil them ... but I would hate to marry a girl who had been spoiled," he said.

Regarding extracurricular activities, parents should choose one sport and one other activity, otherwise, "if you're rushing around doing everything for your child you exhaust your own relationship."

Grant said the maternity leave entitlement of 14 weeks' pay for mothers and the Working for Families assistance was great. But he said the Government should offer more financial assistance, or even tax relief, because parenting was one of the most important jobs.

Auckland fertility expert Dr Neil Johnson said children should be viewed as priceless. It was common for many couples to spend tens of thousands trying to get their dream of becoming parents.