People planning a trip with friends or family often ask whether it's cheaper to book group flights, expecting a bulk discount for buying five or six seats at once. It usually works the other way. Book the whole group in one transaction and every seat can jump to a higher price than the same flight would cost a solo traveler booking alone. The seats didn't get more expensive. You just tripped the fifth-seat surprise.
Why the fifth seat costs more
Airlines don't sell one flat price per flight. They sell seats in buckets, each with its own fare, and they release the cheaper buckets a few at a time. A flight might have four seats left at the low fare and the rest at the next tier up. If you book four people, you all get the cheap ones. Book five in the same order, and the airline won't split you across two prices. It bumps the entire group to the higher fare so everyone matches, because the whole party has to fit in one bucket.
So the fifth person doesn't just pay more. The fifth person drags the other four up with them. On a busy route where the cheap seats are nearly gone, that gap can be real money, the same way a low sticker fare quietly grows once you add the things the price left out.
What to do instead
The fix is boring and it works: don't force one big booking. Split the party into smaller reservations that each land in the cheaper bucket. Two bookings of two and three, or a couple of pairs, will often each catch the low fare that a single block of five could not. You give up the tidiness of one confirmation email, and you'll want to grab seat assignments after so you still sit together, but the per-seat saving is frequently worth it.
Flexibility helps here too. A group of five on a Saturday might blow past the last cheap seats, while the same group on a Tuesday walks right into them, which is the usual reason loose dates beat any coupon.
We don't book groups for you or pretend there's a secret bulk rate to unlock. What Flight Watcher does is watch the real fares on your route every morning, so you can see when the cheap bucket is deep enough to hold the whole party and when you're better off splitting the booking. Read the price for the trip you're actually taking, not the one seat the ad shows.