autos are 5 years MACRS property (double declining balance 1/5 or 20% each year * 2 = 40% on the remaining undepreciated basis switching to straight line when that produces a greater depreciation. The first year is subject to either the 1/2 year or mid-quarter convention) so it takes at least 6 years to fully depreciate it. see IRS pub 946 table A1. Deprecation for luxury autos (ie listed property IRC 280F PUB 946 chapter 5) is limited to a max each year so if you bought a $200K car in 2023 it would take about 26 years to become fully depreciated.
for non-luxury first reduce by any bonus or 179 depreciation -
the remainder if the first year is not subject to the mid-quarter convention (the MQ applies when 40% of cost of certain depreciable assets is put into service in the last 1/4 of the year)
year 1 only allowed 20% under the half-year convention
year 2 100% -20% leaves 80% remaining basis @ 40% =32% on original depreciable basis after bonus/179
year 3 80% - 32% leaves 48% remaining basis @40% = 19.2% on original depreciable basis after bonus/179
for 2023 iRS rev proc 2023-14 determines the maximum depreciation each year for autos
page 6 table 1 if bonus taken
page 7 table 2 if no bonus taken
so when do these limits apply
$12200 - no bonus per table 2 year 1 divided by 20% or times 5 gives us $61000
add $8000 maximum bonus and then the limit would apply to a $69000 vehicle
less than these amounts and it is the 5 year MACRS table rate after any reduction for bonus/179
note that if the vehicle is for hire like a limo or cab then these limits do not apply
