Heathrow Express is offering free travel to the airport at certain times today – so-called Blue Monday.
The initiative came as research commissioned by the rail firm revealed that going on holiday is the top thing that makes people happy.
Holidays and getting something for free came top of the poll of 2,000 adults released to coincide with what is acknowledged as the most depressing day of the year.
Getting a promotion at work and going to the pub with friends are in the top 20 list of activities that make people feel happy.
A third of those surveyed typically feel the least happy in January, and the majority (52%) feel the least happy during winter in general.
Eating comfort food is 12th on the ‘happiness list’ while 42% listen to music when they are feeling sad.
More than a third (37%) call or text their partners when they need cheering up.