A quarter do remember the day but do not give presents or do anything special. One fifth do not even mark it, said a poll for a major credit card brand.
The survey found that most people were "too financially squeezed" to celebrate. A quarter of married couples were still paying for their wedding after three years, according to a leading newspaper.
However, one in 10 people said it was one day they treated themselves and their partner, spending an average amount of money.
Another study by Opinium Research found that 5.5 million never remember the date. Men were twice as likely to forget as women.