Bonus depreciation is an extra first-year depreciation deduction on qualifying business property, applied automatically unless you file a statement electing out, and taken after any Section 179 deduction but before regular depreciation.
The percentage is set by acquisition date. Publication 946’s 2025 revision says P.L. 119-21 “reinstated the 100% special depreciation allowance for certain qualified property acquired and placed in service after January 19, 2025,” with an option to elect 40% instead; property acquired before January 20, 2025 and placed in service in 2025 runs at 40%, or 60% for long production period property. Read the dates carefully — Topic 704 frames that 40% window by placed-in-service date, while Form 4562’s instructions and Publication 946 key it to acquisition, and a trailer bought in December and delivered in February can straddle the line. Topic 704 also puts the allowance “after any allowable Section 179 deduction and before any other depreciation.” General education, not tax advice.
Bonus depreciation and Section 179 are not the same deduction, and treating them as interchangeable can hand you a write-off at the wrong percentage in the wrong year.