For determining the lookback period for garnishments of accounts with federal benefit payments, does the first day of the lookback period begin on the business date before the review date? Or just the date before the review date?

Look at appendix 2

https://www.fiscal.treasury.gov/fsreports/ref/greenBook/pdf/guidelines_garnish0311.pdf

I'm guessing you meant Appendix 4? Yes, I did see this. Thanks.

But none of the examples listed include a weekend or federal holiday as the first day of the lookback period. So, for example, if we receive a garnishment on Monday, 3-5-18, and review the account the same day, does the lookback period begin on Sunday, 3-4-18, or the preceding business day, which would be the preceding Friday, 3-2-18?

Lookback period means the two month period that (i) begins on the date preceding the date of account review and (ii) ends on the corresponding date of the month two months earlier, or on the last date of the month two months earlier if the corresponding date does not exist (e.g. June 31st).

Your example:

Subtract one day: 03-4-18
Subtract two months: 01-04-18

It doesn't matter if they are weekends or holidays.

So its not business days for lookback period purposes, it is calendar days. That is what I was asking. Thanks.

Yes, Appendix 4. Sorry about that.