Wednesday was a red-letter day for many accounting departments, as December 19 was the busiest day for submitting expense reports.

That’s according to expense report software provider Concur, which says it sees more than twice the average daily volume for the year on December 19. In other words, what April 15 is to the IRS, December 19 is to Concur (at least based on its processing volume in 2011).

Processing expense reports can be, well, expensive. According to estimates from Concur and Aberdeen Group, manual expense reporting processes and a desire to reconcile expenses before year’s end contribute to a last-minute rush that could cost U.S. companies more than $2 billion annually.

To better manage this spike in activity, Concur recommends encouraging employees to use mobile technology to capture images of receipts and submit their expense reports via their devices, ensuring expense reports are complete and required receipts are included and adhere to policies, sending out company-wide reminder emails to submit expenses on time, and providing training videos or a Webinar for how to submit and approve an expense report.

It’s also a good idea to remind employees to retain as much documentation as possible of their expenses, especially any receipts. Also they should not try to make up for low salaries and disappointing year-end bonuses by giving themselves an extra bonus by way of an imaginative T&E report.

But then, that’s what the accounting department and their auditors are there to catch.