One of the provisions of the tax law passed in December 2017 is the expansion of bonus depreciation to 100% for qualified property acquired after Sept. 27, 2017 and placed in service before Jan. 1, 2023.
Before the new tax law was enacted, bonus depreciation generally equaled 50% of the cost of the property placed in service in 2017.
This does not mean that assets can merely be expensed though. As with Section 179, assets generally costing more than $2,500 can be expensed in the year placed in service, but the tax return as filed must show the election in order to take it.