Which website tells you the best time to book your flight?

[LynetteScavo]

I want to go to LA for a week in June, adn have heard there is a website that can tell me the cheapest time to buy a ticket.

Does anyone know what it is?

Try skyscanner

Don't know if they have USA flights on there but it's generally a good place to find cheap flights, you can search across a whole month or even a year and it displays prices per day etc.