Probably 1-4 times a month. It depends on the month.
Most of the time, we just eat at home. It's easier. At this point, it's hugely easier for me to throw something together than to go ANYWHERE with the kids (12 and 5). We were on a little outing one day where I'd planned to eat out, and the two kids fought over it, and I said "eff it, we are going home to PB&J".
For me, it's important that I plan these things. We rarely wing it. Okay, so big kid has 3 hours of baseball followed by 4 hours of music practice/ concert? Take him to Chik-fil-a. (I hate that place, so the rest of us don't go.)
We had spring break "staycation" at the end of March, so I planned a couple of meals out (take-out pizza, lunch out of town). When we travel, we generally eat out once/ day, but again - that's planned.
So some months, it might be once a week or even go up to 6 times a month.
Most months, it's much less. My husband will go to lunch with a friend once every few months. I go out for "mom's night" maybe 2x a year. My husband and I do dates occasionally (though last one we ate at home and went to go watch a college volleyball game).
In the end, I guess I'm good enough at throwing stuff together that it's just easier than eating out with kids! Plus we keep frozen pizza from Costco in the back freezer.