Chancellor calls early Budget to fit round Brexit talks
This year's Budget is to be earlier than usual to avoid clashing with the final stage of Brexit negotiations in November.
The date of the Budget, 29 October, also fits in with ministers' availability and official data releases, a Treasury spokesman said.
The Budget will also be a week after a high profile Brussels Brexit summit.
Mr Hammond gave the date in a tweet, saying the government's approach to the economy was "getting debt falling".
The event will be three weeks earlier than last year and will come after a meeting of EU leaders on 18 October in Brussels, described by European Council President Donald Tusk as the "moment of truth" for reaching a deal.
Mr Tusk has also said that "if the conditions are there" an additional summit would be held in November to "formalise" a Brexit deal.
Budgets are traditionally given on a Wednesday.
This year the Wednesday in the final week of October is Halloween, although the BBC understands that this was not a factor in choosing the Monday of that week to deliver the Budget.