There’s a reason many people feel it’s harder to afford children now than in previous generations. It’s true. According to federal data adjusted for inflation, from 1960 to 2015 the average annual cost of raising a child in a middle-income family rose by over $11,000. It’s now estimated that middle-class parents will spend more than $230,000 over the course of their son or daughter’s childhood — and that doesn’t even include college tuition.

Ask just about any couple and they’ll tell you this absolutely influences their decisions about when to have children and how many to have. As the economist Lyman Stone has shown, by 2012, the average number of children American women intended to have was 2.37, and the total fertility rate was 1.88 — a gap of about 0.5 children on average. Since the 1960s, there has been a consistent gap between intended and total fertility, even as the number of children American women desire to have and the total birthrate have declined over time.