Tax season is a miserable time of year for many, but some credit unions are gleefully looking forward to those filing deadlines — and building profitable new revenue streams while they're at it.

At the Raleigh, N.C.-based State Employees' Credit Union, for example, tax preparation services are growing by 15% a year, according to SVP of Tax Preparation Services Tenesha Carter. At the $3 billion, Herndon, Va.-based Northwest Federal Credit Union, tax preparation at a subsidiary of its wholly owned CUSO, NW Capital Management, has been a profitable revenue source since it started offering the service in 1997, according to the CUSO's president/CEO, Kevin Fisher. Today the Northwest Tax Group subsidiary handles about 900 tax returns a year compared to about 750 per year five years ago, Fisher said, and 94% of its clients are repeat customers.

Many credit unions offer tax preparation services by participating in the IRS's Volunteer Income Tax Assistance program, or VITA. The program provides matching grants to nonprofits and coalitions that give free tax help to qualifying taxpayers — typically the disabled, those who made $54,000 or less in 2015 or those with limited English proficiency.