How it works
Month 1 is the month the baby is due. Each parent gets their leave pay for their first leave months and their usual take-home after that. Spending each month is your usual spending plus baby costs (the hospital bill in month 1, later gear in month 6, the monthly costs every month) plus childcare from the month it starts. The gap (spending minus pay) comes out of savings. Savings on the due date are what you have today, plus what you can still save each month until then (pay minus usual spending), minus the gear you buy before the birth. The extra to save is how far the lowest point would go below $0. The spreadsheet does the same with every item in its own month, gifts, and a warning when parents' pay doesn't add up.