Calculate First Day Of Previous Month
VB/VBA/VB.NET one-liner to calculate the start of the previous month. Useful for SSRS/RDL Expressions and Excel/Office Formulas. Note that it does not use string parsing, which can cause localization problems.
DateAdd("D", -1.0 * DatePart("D", Today) + 1, DateAdd("m", -1, Today))