It is still hard to say when the credit will get cut in half. The day Chevy sells/leases the 200,000th electric car starts the countdown to the day that the credit gets reduced. But it is kind of complicated. The credit is reduced at the beginning of the SECOND quarter after the one in which the 200k car was sold. So if GM sells its 200k'th car on June 15th 2018, they would be just 15 days from the end of the quarter so the credit would be reduced as of October 1st, 2018. But if they sell the 200k'th car on July 15th, 2018, they get the full credit until January 1st 2019. PLUS, they can sell an unlimited amount of electric cars between the time they sell the 200k car and the reduction of the credit, 3 to 6 months later. Can you imagine how good the deals are going to be in that 3-6 month timeframe? GM will know that they are going to have to reduce the price of the Volt/Bolt/CT6 by $3750 a couple months later to get the sales to stay strong, so they will probably be dropping the price by $2k to $3k to run up to the reduction strong.
Right now GM has sold around 104,000 Volts, 7,000+ Spark EV's and nearly 3,000 ELR's. So say 114k. October, November and December will see around 9,000 Volts and a several hundred Bolts/Sparks/ELR's sold. Around 124,000 electric cars total. 2017 will see around 55,000 Bolts/Volts sold. So 179,000 going into January 2018. Winter electric car sales are lame, so January, February and March of '18 will probably only add 12,000 to get us to 191k. So GM can continue to sell an increasing amount of Bolts in the second quarter and lose the full credit on October 1st of 2018, or they can have an "inventory shortage" and sell the 200k'th car in early June and keep the full credit through the prime electric car sales months of October, November and December, thereby allowing the full credit to run out in January of 2019.
What do you think will happen?
https://www.fueleconomy.gov/feg/taxevb.shtml