there are actually 3 methods for computing wages for the qbi dedication
this is from notice 2018-64
SECTION 5. METHODS FOR CALCULATING W-2 WAGES
For any taxable year, a taxpayer must calculate W-2 wages for purposes of section 199A(b)(2) using one of the three methods described in section 5.01, 5.02, and 5.03 of this revenue procedure. For a taxpayer with a short taxable year, see Section 6 of this revenue procedure. In calculating W-2 wages for a taxable year under the methods below, the taxpayer includes only those Forms W-2 that are for the calendar year ending with or within the taxable year of the taxpayer and that meet the rules of application described in section 3 of this revenue procedure..
01 Unmodified box method. Under the unmodified box method, W-2 wages are calculated by taking, without modification, the lesser of—
(A) The total entries in Box 1 of all Forms W-2 filed with SSA by the taxpayer with respect to employees of the taxpayer for employment by the taxpayer; or
(B) The total entries in Box 5 of all Forms W-2 filed with SSA by the taxpayer with respect to employees of the taxpayer for employment by the taxpayer.
.02 Modified Box 1 method. Under the Modified Box 1 method, the taxpayer makes modifications to the total entries in Box 1 of Forms W-2 filed with respect to employees of the taxpayer. W-2 wages under this method are calculated as follows—
(A) Total the amounts in Box 1 of all Forms W-2 filed with SSA by the taxpayer with respect to employees of the taxpayer for employment by the taxpayer;
(B) Subtract from the total in paragraph .02(A) of this section amounts included in Box 1 of Forms W-2 that are not wages for Federal income tax withholding purposes, including amounts that are treated as wages for purposes of income tax withholding under section 3402(o) (for example, supplemental unemployment compensation benefits within the meaning of Rev. Rul. 90-72); and
(C) Add to the amount obtained after paragraph .02(B) of this section the total of the amounts that are reported in Box 12 of Forms W-2 with respect to employees of the taxpayer for employment by the taxpayer and that are properly coded D, E, F, G, and S.
.03 Tracking wages method. Under the tracking wages method, the taxpayer actually tracks total wages subject to Federal income tax withholding and makes appropriate modifications. W-2 wages under this method are calculated as follows—
(A) Total the amounts of wages subject to Federal income tax withholding that are paid to employees of the taxpayer for employment by the taxpayer and that are reported on Forms W-2 filed with SSA by the taxpayer for the calendar year; and
(B) Add to the amount obtained after paragraph .03(B) of this section the total of the amounts that are reported in Box 12 of Forms W-2 with respect to employees of the taxpayer for employment by the taxpayer and that are properly coded D, E, F, G, and S.
