All of the vouchers I have purchased in the past have been good for a year.
I bought a voucher from
IT Exam Vouchers - Discount Certification Exam Test Vouchers back in late February.
Per their website
Our exam test vouchers have an expiration of up to one (1) year. Check out our Specials page for short life vouchers that save you even more!
I bought a regular voucher. The voucher I was given apparently expired just 4 months after it was issued. I went to schedule an exam and was told my voucher was expired. I went and found the receipt. I'm kind of upset because the voucher cost me $120.
I told them I wanted my money back or a new voucher. What says you?
For instance at
http://www.measureup.com/Site/display_article.aspx?id=1688
they say vouchers are good for 9-12 months.