More babies will be conceived tomorrow than any other day this year, according to new research.
National birth records show that September 16 is the most popular birthday in the UK.
And with the average gestation period for a baby being 40 weeks December 11, exactly 40 weeks prior to September 16, has been labelled as the most fertile day of the year.
Planning a baby? Make sure you have sex on December 11th - it's officially the most fertile day of the year
December is also the most popular month for conceptions – 9 per cent of babies are conceived then - and the ten most popular birthdays in the UK are all in September.
Scientists say that winter is a more fertile season than summer because sperm quality is higher in the cold.
People also have more sex in December than other winter months because of festive partying and end-of-year happiness.
Famous people born on September 16 include the actor Mickey Rourke and the singer Katie Melua.
The statistics were compiled by Lovehoney, Britain’s biggest online seller of sex toys, based on established scientific studies.
The Christmas party season has a big influence on conception rates
Lovehoney co-founder Neal Slateford said they were expecting a huge boom in sales prior to December 11.
He said: 'December is always one of our busiest month as couples treat each other at Christmas.
'Everyone is increasingly doing their Christmas shopping online - who wants to go out to the shops when it is pouring down and there are queues at the check-outs?
'So we are expecting a big surge ahead of December 11, the most fertile and sexiest day of the year, when I guess a lot of broody couples will be staying in and having a good time!'
Bath-based Lovehoney compiled the statistics as it celebrated record sales in 2012, thanks to Fifty Shades of Grey for which it has developed the official range of pleasure products.
Turn-over shot up by a third, driven by a record demand for toys such as the silver balls featured in the E L James trilogy.
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