Start-up costs are claimed in the first year the business is "open for business". It does not matter in what year those startup costs were incurred.
Start-up costs that can be claimed in that first year are limited to a maximum of $5,000. The maximum for that first year reduces if the business exceeds a certain income threshold in that first year. This is not all that common. Any remaining startup costs exceeding the maximum allowed that first year are amortized and deducted over the next 15 years of business.
The maximum allowed that first year "may" have changed for all I know. But $5K is what it was last time I looked it up.
