The UK's Coral bookies make it 1/2 that Kate will make a pregnancy announcement before the year is out.
Coral spokeswoman Harry Aitkenhead said: “On Prince George’s sixth birthday there’s been plenty of talk about whether William and Kate will add to their family.
“We think a fourth baby is very likely and make it odds on that the Duchess of Cambridge announces she is expecting again by the end of this year.”
Kate whipped fans into a frenzy over speculation she may already be pregnant with her fourth child during her appearance at Royal Ascot last month.
The Duchess of Cambridge was spotted on several occasions throughout the day holding her stomach - often a subconscious move made by mums-to-be.
William and Kate are already parents to Prince George, six, Princess Charlotte, four, and one-year-old Prince Louis.
