Best way to find the cheapest flights online?

I use Kayak 3-4 months before my trip, and leverage the flexible search options: first by departure month + trip length to get an idea of fares, then narrow down using +- 3 days departure/arrival to find the actual best flight for me.

With this method I typically find reasonable fares all year round (~$400-$700 round trip US/EU, ~$200-$400 round trip US) with maximum one stop and maximum 2-3 hours layover (less if domestic). The key is being flexible with the days. Being flexible with specific days easily finds you good prices even during hot season, say Xmas or summer.

I’ve been using Kayak for 10+ years of international flights, easily booked 50+. Neither Google Flights nor ITA Matrix nor the other search engines work as well in my opinion.

Occasionally I sign up for credit cards and get the 80,000 miles bonus, but those are generally a pain to effectively use, there are always so many restrictions that paying $500 cash to go to Europe ends up a better use of my time.