Talk to your friends and find out what their bills look like. If both parents have been working, the biggest question is whether one of them will stay at home with the baby. The alternative is using a daycare arrangement. Many parents are surprised at how little money is actually earned by the second breadwinner when expenses are deducted. It involves much more than just money.
Some parents are very happy staying home with children.
Others are not. Career plans, the pace of family life, baby's health and more can all be affected by the choice you make. Once you've made that decision it's time to look at a proposed budget. If a family is used to spending all of the current income, some adjustments will be required. You can't take a budget that's tight now and shoehorn in the extra expenses of a baby.