Up to 20 US states are considering a law to make equally shared custody the default arrangement in divorces and separations, after pioneering legislation in Kentucky was followed by a large drop in divorces.

The southern state passed its law in 2018 and Four other states—Arkansas, West Virginia, Florida and Missouri—have since passed their own versions of the bill, not least because of its effect on marriage.

Between 2016 and 2023 Kentucky’s divorce rate fell 25%, compared with a nationwide decline of 18%, according to an analysis by the National Center for Family & Marriage Research at Bowling Green State University. They say the additional effect is because mothers and fathers gain equal custody over the children, whereas usually the mother gains custody. Most divorces are initiated by women.

Matt Hale, vice chair of the National Parents Organization, said “Giving kids equal access to both their parents is just common sense.”

The drop in the divorce rate is, he said, an unintended bonus of the custody law.

He suggested that parents are increasingly likely to stay together because they realise they’ll be in regular touch regardless, so “they might as well work it out.”

He added that he’s heard stories of couples who decided not to break up because of the presumption of shared custody, and years later are glad they stayed together.