Current annual income is defined as what you expect to earn over the next 12 months from the date of submitting the I-864. That would include all sources of expected income. Current annual income is not derived from tax returns (unless you are self-employed). It is derived from what your income will be for the next year after the new immigrant arrives.
Rationale: You will be supporting the new immigrant with income over the next year...not what was earned last year.
W2s are supporting documents for past tax returns...not for future income.
Current annual income- Continuing Pay statements, pay stubs, and employment letters are documentation for current and expected income.
-Example: Current annual income = gross pay from most recent pay stub multiplied times the number of pay periods per a 12 month period.