Jennie Garth is getting real about life after “Beverly Hills, 90210” … and the money mistakes she still regrets.

On Dax Shepard’s “Armchair Expert,” Jennie admitted she never really thought about finances back in the day — cash was flowing in, she was spending, and she figured it would just keep coming … until it didn’t.

When the show ended, reality hit hard — Jennie says it was a serious adjustment once the paychecks stopped rolling in.

Watch the video … she says it got worse — she revealed her business manager basically scared her into selling the home and ranch she’d just bought for her kids … a move she made, and now deeply regrets.