Take advantage of the three-day flex search
Once again, if your travel dates are flexible, your chances of finding a cheap flight are much, much better. When you're looking up airfare, before you hit Search, click “Show flexible dates” to pad the timing of your departure and return trips up to three days on either end. This way, when you search you’ll see prices neatly plotted on a handy grid, making it extra easy to spot the cheapest dates to fly.
Scope out Kayak's Travel Hacker for popular destinations
Before you book your next vacation, scope out the Travel Hacker section. Using data collected in the billion-plus searches it processes every year, Kayak curates lists of the most popular destinations, arranged by theme (Luxury, Family, Beach, etc.), then builds custom cheat-sheets for each destination. So, for example, if you pop into the top Luxury destination of the moment (right now it's Medellin, Colombia) it shows how airfare and hotel prices fluctuate over the course of the year, so you can identify the best time to book at a glance. And if you’re booking a trip over Christmas or New Year’s, there’s a dedicated Holiday Travel Hacker section as well.