On the older ones, emisions test is good for 11 months. Not sure about the new ones. I just bought an older one and missed the deadline by one week.
If the vehicle is less than 6 years old, emission tests are every 2 years. If the model year ends in a odd #, then you test in an odd year; and vice versa. (IE 2015 Honda civic will need an emissions test this (2019) year.) Older than 6 years (IE 2019 - 6= 2013 and prior), emissions need to be done every year. All the way back to '68 models.
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