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Women tend to be less fertile as they get older, but how much, exactly? Math nerd Richie Cotton at 4dpiecharts.com decided to figure it out with a chart.

Cotton, who is trying to have a baby with his girlfriend, used data from the Journal of Human Reproductie Sciences and Social Fertility to figure out "monthly fecundity rate," or likelihood of getting pregnant each month if you're having sex without birth control. A healthy, average woman of 25 has an MFD of 25 percent. MFD decreases to 10 percent for a woman of 35. He then put the data in some formulas to plot out the chart.

According to the chart, after two years, nearly all 25-year-old women will get pregnant. The older women get, the less steep their dotted lines get. In other words, the graph visualized what we already knew: It takes longer for older women to get pregnant. While the gap between 25-year-old women's baby pink line and 35-year-old women's green line is not too bad, the five-year difference between a 40-year-old and 45-year-old is striking.

The same chart for men, on the other hand, would look very different, Cotton says. "From a male point of view, conception is an embarrassingly parallel problem: you can dramatically reduce the time to conceive a child by sleeping with lots of women at once."

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