Stripe Atlas supports two options for forming a US company in Delaware: C Corporations and Limited Liability Companies (LLC).
When to form your company
If you plan to form your company near the end of the calendar year, it can make sense to wait until the start of the new year to form your company because of the tax implications. C Corporations active in Delaware any time before December 31 owe at least the minimum Delaware franchise tax for that year. LLCs active before December 31 owe the full annual LLC tax for that year.
Neither the franchise tax nor the LLC tax is prorated. Your company might also owe US federal corporate income tax for the outgoing year. It might also owe taxes to a US state other than Delaware, depending on where the LLC operates.