sungod wrote:this is the place to do it... https://esta.cbp.dhs.gov/esta/
if you will not travel before april, i'd leave it until a week or so before
That is very risky - if you are not automatically approved & need to visit the US Embassy, then the odds of getting an appointment within a week is probably zero. I can't see any travel insurance paying out because you failed to get the correct documents, i.e. ESTA approval, in good time.
I always do my ESTA a couple of months in advance, just in case. Since ESTA was introduced I have always been approved instantly - but I do not take this for granted. No doubt the USA re updating their lists of "no fly" / "do not admit" people on a daily basis - all you need is a name and / or date of birth to match.
Tonty - thanks for the link to that tool, checked out my I-94 entries on my passport and they're all correct (phew!) each arrival has a subsequent departure.