Getting your Trinity Audio player ready...

Don’t stock up on silver anniversary cards. More than half the Americans who might have celebrated their 25th wedding anniversaries since 2000 were divorced, separated or widowed before reaching that milestone, according to a census survey released Wednesday.

“We know that somewhere between 40 percent and 50 percent of marriages dissolve,” said Barbara Risman, executive officer of the Council on Contemporary Families, a research group. “Now, when people marry, everyone wonders, is this one of those marriages that will be around for a while?”

The survey by the Census Bureau, in 2004, confirmed that most Americans eventually marry, but they are marrying later and are slightly more likely to marry more than once. While the latest numbers suggest an uptick in the divorce rate among people married from 1975 to 1994, the proportion of all Americans who have been divorced, about one in five, remained constant.

In 2004, among people in their late 20s, a majority of men — 54 percent — had never married, as had 41 percent of women. In 1996, the comparable figures were 49 percent among men and 35 percent among women.

In the latest analysis of people age 15 and older, 58 percent of women and 54 percent of men had married only once. In 1996, the figures were about 60 percent for women and 54 percent for men.

The oldest Baby Boomers recorded the highest divorce rates. Among people in their fifties, 38 percent of men and 41 percent of women had been divorced.

One statistical constant has been the so-called seven-year itch, as popularized in the play and film about errant husbands. Couples who separate do so, on average, after seven years and divorce after eight. The duration of first marriages that end in divorce appears to have increased slightly among men.

Among adults 25 and older who had been divorced, 52 percent of men and 44 percent of women were currently married.

On average, people who remarry typically wed again in about 3.5 years. Second marriages that end in divorce last about 8.6 years for men and 7.2 years for women.