Babies are game changers, no matter how old you are when you have ’em. But, according to science, there’s an actual age at which you’re better off conceiving if you want your kid to be a genius.

It’s your 30s. (Cue the debate.)

The study, out of the London School of Economics, looked at data tracking the development of 18,000 British children over their first five years of life. The conclusion? Women who become moms in their 30s typically have smarter babies (based on cognitive testing) compared with women in their 20s and 40s.

Here’s why: First-time 30-something moms are more likely to be educated, have higher incomes and be in stable relationships. They’re also more likely to seek out prenatal care and plan their pregnancies, according to researchers.

So go ahead and store this gem in your back pocket for the next time your mother gives you crap about not procreating sooner. You’re just holding out for a clever son or daughter, after all.