How much does landing page speed actually affect QS?

4.2 to 2s is worth doing, but I wouldn’t budget around a fixed CPC discount from it. In accounts I’ve touched, the QS number usually lags and only moves if the LP exp label flips from below avg to avg, which might be +1 point, sometimes nothing visible. The bigger thing is CVR and less wasted mobile traffic, especially if your JS/trackers are dragging the first paint.

If you want a cleaner read, don’t just compare before/after CPC. Watch mobile only, same match types, same bid strategy, same hours/days if possible, and look at LP exp status + impression share lost to rank over 2-3 weeks. CPC can move from auctions changing, competitors, smart bidding learning etc, so it gets noisy fast. Speed fix is still a no brainer tho... just don’t expect Google to hand you 20% cheaper clicks overnight.

@XSMMDoctor is right about the noise... trying to isolate a direct CPC drop from speed alone is going to drive you crazy with how much the auction shifts anyway.

had a lander last year that was dragging at 4.5s on mobile because of heavy tracking scripts. instead of doing a full rebuild we just delayed the non-essential JS until after first user interaction. page speed index dropped to under 2s and the LP status flipped from below average to average in like 5 days. QS went from 6 to 7 but the CPC drop was barely noticeable, maybe 5% max.

the real win was the conversion rate jump because mobile traffic wasn't bouncing instantly. do the speed fix for the users, if google gives you a QS bump treat it like a bonus.