A business generally faces several taxes at once, each with its own rules, authority and deadline.
The ones a service business meets
Income tax on profit, paid by the business or passed to the owners depending on structure — see business entity types and estimated tax payments.
Payroll taxes — withheld from employees and paid by the employer, with the strictest deadlines of the group because the money is held on someone else's behalf.
Sales tax — collected from customers and forwarded. Never the business's revenue.
Property tax on premises and, in some places, on business equipment.
Franchise or business privilege tax — charged in some states for the right to operate there, sometimes owed even in a loss-making year.
Excise taxes on particular goods, activities or fuels.
Deductions and credits
A deduction reduces the profit that is taxed. A credit reduces the tax itself, so a credit is worth considerably more than a deduction of the same size.
Credits exist for particular activities — hiring from certain groups, energy efficiency, research — and they change frequently. They are worth asking an accountant about specifically, because they are easy to miss and are rarely volunteered.
Where the business owes tax
Obligations follow activity, not just address. Working across a state line, storing goods there, or having staff there can create a filing obligation in that state.
This is the nexus question, it has grown more complicated, and it is a genuine risk for businesses that expand their service area — see geographic expansion.
Deadlines
Separate for each tax and each authority. Penalties commonly attach to late filing as well as late payment, so a return with nothing owed still costs money if it is late.
Corrections
Where a return was wrong, it is amended rather than adjusted quietly in a later period.
The boundary of this article
It describes the categories so the vocabulary is familiar. Rates, thresholds and eligibility change annually and by jurisdiction, and belong with an accountant — see tax preparedness.
Where a business owes tax in more than one state, apportionment is the method deciding how much of its income each state may tax, generally weighted by sales, property or payroll in that state.