The Centre for Retail Research, based in Nottingham, central England, estimated an extra £243 million in sales in July and August.
It predicted £87 million spent on royal baby celebrations much of it on alcohol £80 million on toys and souvenirs and £76 million on books, DVDs and newspapers.
Tourism officials said that while it was difficult to put an exact figure on the likely baby boost, Britain’s cultural heritage as embodied in the royal family boosted the economy by £4.5 billion a year.
“While a living royal family gets us an enormous amount of free advertising for Britain around the world, it’s not really something we can estimate a figure for and the international coverage alone is priceless,” a Visit Britain spokesman said.
“We know that visitors drawn here by the appeal of our culture and heritage spend over £4.5 billion annually and support around 100,000 jobs,” the spokesman added.
“Some of that figure can be attributed to attractions and events with a connection to Britain’s monarchs past and present.”