Using PREVIOUSMONTH works for most cases but need conditional logic for January only

Hello,

The previousmonth function captures what I need for 11 out of the 12 months of the year.  January is the special case which needs to be handled differently.  My formulas:

Incurred = ActualSpend - ActualSpend_PrevMonth

ActualSpend_PrevMonth = IF(ISBLANK([Max Spend]), 0, CALCULATE([Max Spend], PREVIOUSMONTH('Calendar'[Date])))

Incurred_jan = CALCULATE([Max Spend], FILTER('Calendar', 'Calendar'[Date].[Month] = "January")) -MAX(SomeOtherSpreadsheet[ITD Actual To EOPY])

There's an actualspend value for January but i need to subtract it from a starting value to figure whats actually been spent in January.  

Is there an easy way to merge the outputs so I can visualize it on a barchart/table?   Essentially I need that January value with the rest of the data. 



Thanks!