Timesheet and V-Look ups

I've attached a sample time sheet for the expert(s) to view.

On the Time Card tab, when I enter the week-ending date (which always falls on a Saturday), I want the appropriate week# to populate. These are managed by the tab 'Calendar 2012-2013'.

For instance, this year 2014, the week ending of 1/4/2014 is Week 1.

On the Calendar 2012-2013 tab, when I change the dates and week numbers, they don't populate as they should on the time sheet tab.

How can I make this work? I am terrible at v-lookups and formulas

That worked - thank you!