Question: I plan to invoice in 2018 consulting services rendered 2018 but will be paid in 2019. Which tax year is this considered income?

[Opus 17 · Accepted solution]

Unless your business operates under the accrual accounting method (uncommon, and you would have needed an accountant to help set it up), then you are a cash basis taxpayer.  Expenses are recorded when you actually pay them and income is recorded when you actually receive it.