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President Barack and Michelle Obama will observe their 17th wedding anniversary in October. For country music superstars Faith Hill and Tim McGraw, this year marks lucky (or unlucky) number 13.

Men and women who say “I do” today are less likely to reach significant anniversaries than were couples from previous generations. The odds that a female first married between 1955 and 1959 reached a 10th wedding anniversary are 1 in 1.15 (or 87%). For women first married in the 1990s, however, the likelihood dropped to 1 in 1.45 (69%).

Husbands and wives hoping to toast to 25 years of marriage face tougher odds. While 1 in 1.49 (67.1%) women first married between 1955 and 1959 reached a 25th anniversary, the odds for women first married between 1975 and 1979 were 1 in 2.16 (46.3%). And with marriage rates in the United States declining (7.5 per 1,000 total population in 2006, down from 9.8 in 1990), couples standing the test of time have all the more cause for celebration.

One of the most cherished anniversary traditions is the giving of gifts between spouses. According to custom, husbands and wives exchange gifts of paper to commemorate their first year of marriage, while veterans of the institution swap china to honor 20 years of wedded bliss. Couples reaching their 50th—known as the “golden” anniversary—are eligible for a special treat: a personalized greeting card from the President of the United States, which can be requested in advance from the White House Greetings Office. Herbert Fisher, 104, and his wife Zelmyra, 101, of North Carolina, received both a citation and an invitation to the White House from President Obama when they celebrated 85 years of marriage on May 13, 2009. They have been recognized as the longest-married couple in the world.