I had this misunderstanding when I first got my IDP a couple of months ago that I thought it could last the entire year till February 2012 but I was wrong.
Yes, the validity of the IDP is for a year from the date of issue. However, it is not just that. A closer scrutiny of the rules revealed that the IDP is valid for:
1) a year from the date of issue or
2) a year from the date of embarkation whichever is earlier
So it doesn’t matter when you apply for the driving permit, if you’re going to be a resident in Japan, your right to use the IDP begins from the date you step onto Japanese shore. That would mean getting the IDP before flying over is a better bet. It’s only $22 anyway. There’s a way out of this though, which is that if you leave Japan from more than 3 consecutive months, your IDP becomes valid again from the day you return to Japan. But how do they know? Good question. When driving with an IDP, you don’t just bring your IDP with you. You must bring your passport too.
Unfortunately for Singapore males, if you return home for 30 days or more, you’d have to reapply for the exit permit. The good news is, applying for the exit permit is really an easy process. You don’t have to submit any documentation unless asked, which I believe is pretty seldom since they only do occasional random checks.
With this, I hope none of you get caught by the traffic police driving without a valid IDP and get barred from driving in Japan.