Here’s an article at CNN, which is dishonest but probably not yet quite brazen enough to lie outright about a House member retiring.
43 House Republicans and 19 House Democrats have announced plans to retire or have retired. The Republican House majority right now has a margin of 48, so Democrats need to flip 24 House seats to retake the majority. (Each time a seat changes party, the old party loses a seat and the new party gains a seat, so flipping one seat changes the party margin by two.)
I don’t know the odds of a seat changing parties when someone retires. So I’m just going to assume that half of such seats switch to the opposite party. This probably overstates the frequency of a party change, since the whole reason that a seat is Republican or Democrat in the first place is probably that that district leans Republican or Democrat. But just to get a feel for the basic idea…
If the probability of a seat changing parties is one half, then with 43 Rs retiring and 19 Ds retiring, the Reps lose 21 and the Dems lose 9 (rounding down). So the R net loss is 12 and the D net gain is 12, for a net change of 24. That’s not enough to flip the House by itself: the Dems need to flip 24 seats for a net gain of 48, not flip 12 seats for a net gain of 24. Still, it sets up a headwind for the GOP in the battle for the House.
All this said, it’s important to note that some of these people are retiring from the House in order to run for a Senate or Governor position.
What about the Senate? Per USA Today, there are three GOP Senators retiring, and no Dem Senators retiring. But the Dems are defending a lot more Senate seats than the Repubs overall, so no one is predicting the Dems will take the Senate.
Also, those three retiring GOP Senators are Orrin Hatch, Bob Corker, and the aptly-named Jeff Flake, all of whom would have been defending their Senate seats this year anyway. In other words, these aren’t surprise mid-term retirements that make an otherwise-safe seat contestable. They were slated to be contested anyway. Flake, BTW, is an anti-Trumper, so losing him isn’t a hell of a loss. Orrin Hatch is simply a Washington D.C. creature, and I don’t know about Corker.
Note: The Infogalactic page on the House hasn’t been updated in years! As of this writing, May 21, 2018, it says that the “Next election” will be in November 8, 2016. Duuuuur. Come on, guys. So here’s the Wikipedia page: