Those who live in rural areas will pay about 6 percent less overall than the average urban-area couple because housing costs are so low. Rural families spend more on transportation and medical care possibly because of greater distances to be traveled and lack of competition among medical providers.

What have swelled are child-care and education costs, from 1 percent of household spending in 1960 to 10 percent today. Dr. Mark Lino, a USDA economist, says the increase reflects a surge in the number of households in which both parents work.

A second child does not double your expenses. The new child will cost about 20 percent less than the first because you can take advantage of hand-me-down clothing and nursery furniture. You might be able to have your children share a bedroom, or carve a second bedroom from an existing space, effectively driving down your per-child housing costs. For obvious reasons, parents of multiples enjoy fewer economies of scale.

Single parents (now about 30 percent of all families with children under 6) have it tougher all around. Those who earn more than $40,000 will spend about 29 percent of their income each year on a child, while two-parent households earning the same income will spend just 15 percent of their earnings on their kid. Lower-income single parents will spend only a little less for most of their child's needs and, surprisingly, a lot less on child care, possibly because they tap relatives to baby-sit.

The percentage of income that parents lavish on children diminishes as income rises, though the actual dollar amount will soar. A couple with one child, born in 2002, taking in less than $39,900 annually will spend about $158,000 over 17 years, or about 35 percent of annual earnings. A couple with a combined annual income of more than $66,900 will spend about 17 percent of income, a total of $315,000, by the time their child turns 18.

Baby Tax Breaks

The federal government has taken some baby steps to ease parents' burden. A new tax bill signed into law in May gives parents a larger tax write-off on minor children. Starting this year, the current child tax credit of $600 (which is subtracted directly from your tax bill) will be immediately upped to $1,000 for each child under age 17, as long as the family income is less than $110,000 ($55,000 for single filers). That comes on top of a somewhat more generous personal exemption, up from $2,800 to $2,900 in 2002. Working parents may also qualify for the child-care tax credit, which allows them to deduct 20 to 35 percent a year of up to $3,000 in day-care bills for one child (up to $6,000 for two or more kids), depending on income.