William, 28, and Harry, 26, will be joined by more than 20 friends at a location outside London, The Sun reported.
The groom had reportedly insisted the party had to be in Britain.
A source said: "They would have held it closer to the wedding day of April 29, but William was keen to make sure there was a big-enough gap before the big day."
"Harry has planned the stag do in great detail," the source added.(IANS)