This reason for the City of Seattle's gender wage gap may surprise you

April 11 was a rather unfortunate holiday: Equal Pay Day.

It's the day when a woman's salary catches up to what the average man earned in the previous calendar year. That amount of time is pretty reliably 15-16 months to a man's 12, and there are some surprising reasons for why the numbers have been so stubborn, says David Kroman in a piece for Crosscut.

As growth squeezes Seattle, overstrapped city departments have struggled to keep up with demand. Rather than hiring more workers, some departments, such as City Light, rely heavily on overtime to bridge its gaps in capacity.

Workers can triple their salaries with overtime, in some cases. And overtime-eligible positions are disproportionately filled by men. Under Mayor Ed Murray, the city had been touting a 90% equity rate. But when overtime pay was factored in, the amount women make fell to 78 cents on the dollar - just a penny more than the national average.

Overt discrimination is something that's easier to deal with, for a committed manager. But Kroman says that in order to close that stubborn gap, we may need to go deeper, rethinking the nature of what we consider men's or women's work.