If you're getting X% merit increases every year and miss one, it will look forever as if you're underpaid relative to your peers. So people who take a long parental leave will have a permanent "pay gap" unless either the company pro-actively bumps them up (pay for the absent time as if they were present) or the employee overachieves to catch up (in which case they still have a pay gap relative to their overachieving peers).

Of course, there's also ramp-down and ramp-up time on each side of the leave. I'd expect a leave of 12 months is probably closer to a total productivity loss of 18 month, which will drag pay down further if there's a reduction to a second merit increase. If you take years off, as many do, staying home until the kid enters kindergarten, then you're probably looking at a massive relative gap when you start back.

But yeah, taking a year for parental leave is not a death knell for most professionals' careers. It will realistically result in a long-term salary depression relative to peers, though.

Since I started out working for startups, I guess I'm used to people changing jobs so often that you can't really generalize about salary like that. Like, I can't imagine judging someone by their previous or current salary versus age. (Or even knowing either data point with much precision.)

You're right that it's not cut-and-dry. A year out of the workforce doesn't guarantee a lower salary for any particular individual. It does bias toward a lower salary, though. This is the case whether you're job-hopping or not.

For women it makes a big difference as there is generally a choice to make between 25-35 as To whether they’d like to further their career or take time out to have a child.

Most women also reasonably choose to prioritize family over career when their children are very young further inhibiting them from advancing their career during that time.

I wish this were true, but in technology (my field) one year can make you fairly outdated and unprepared to perform strong interviews. And in some tech industries such as frontend web development, one year is practically a lifetime.