I clipped out a chart from a 2013 Kayak study of pricing which shows some optimal points to book flights:
We're going in late August 2015 so I'm thinking of booking around June.
Also Google flights can show lots of data in an easy to view way. As an example, click on this link and then clink in the August 27 box which will show you flights costs by days for August and Sept. This is useful if you are flexible. Link to click: https://www.google.com/flights/#sea...9-21;s=0;q=flight+sfo+to+ams+february+10+2015
Ah, to be retired. I wish I could book a trip only two months in advance. I usually end up paying extra because we have to juggle time off from work with kid's breaks. The problem with these big trips with family is that you don't want to figure out all the details with only two months before you leave. Especially if you have certain fixed criteria that you need to meet (yes, we're going to Rome, Paris, etc). I also look forward to being able to travel in the off season, spring or early fall. A few more years before this becomes a reality for us, but this is on top of our 'what are we going to do all day' list when we finally pull the plug.