As airlines slap travelers with separate charges ranging from baggage fees to fees for switching to a better seat or boarding the plane early, Concur has tweaked its expense management software to help companies track those costs.

Over the last six months, 2.3% of Concur's customers' overall spending with airlines has consisted of such ancillary fees, says Ellen Trotochaud, senior director of analytics and travel supplier relations at Concur. Just two years ago, she says, the only airline fees companies usually encountered were those for changing tickets, which were buried in the cost of the ticket.

The International Air Transport Association says airlines will take in about $58 billion in ancillary fees this year, Trotochaud notes. "Just baggage alone is targeted at about $4 billion. That's a lot of spend."