THESE days, many prosperous baby boomers are subsidizing parents, and sometimes siblings, who are less fortunate. Innocuous as this may seem, being generous can also subject you to gift tax. While helping a family member often occurs under the radar, if the gift exceeds a certain value and the I.R.S. catches it, you could be forced to pay the tax as well as interest.

Nancy G. Henderson, a trusts and estates lawyer with Henderson & Caverly in Rancho Santa Fe, Calif., has advised clients on these issues and dealt with them in her personal life. After her mother developed health problems in 2002, Ms. Henderson suggested she move west from Dallas and live closer to family. Trouble was, her mother, Anita Gundermann, 80, couldn