While Chancellor Philip Hammond will unveil his proposals in a statement to the House of Commons on Monday October 29, MSPs will not discover what the Scottish Budget will be until Wednesday December 12.
Mr Mackay took to Twitter to confirm when he would deliver his third Budget.
Scottish Conservatives had previously called for the Finance Secretary to make the announcement in mid-November - suggesting three weeks from the Chancellor’s Budget is enough time for Mr Mackay to draw up his plans.
Tory finance spokesman Murdo Fraser argued: “This would allow Parliament to have far more time to analyse his Budget, as opposed in previous years when we’ve had barely any time to study it before recess.”
But Mr Mackay said the Chancellor had only given the country five weeks’ notice of when the UK Budget would be, instead of the normal 10.
He added that the date for the Scottish Budget had been agreed with Holyrood’s Finance Committee, taking into account the need of other committees to complete their pre-Budget scrutiny processes.
The Finance Secretary said: “The Scottish Government will present the 2019-20 Scottish Budget to the Scottish Parliament on Wednesday December 12.
“In normal circumstances, the Scottish Government is provided with 10 weeks’ notice from the UK Government of its Budget date, however the announcement by the Chancellor on September 26 provides less than five weeks’ notice of the date of the UK Budget.
“The Scottish Budget date of December 12 has been agreed with the Scottish Parliament’s Finance and Constitution Committee to allow due consideration of the necessary 10-week Scottish Fiscal Commission lead times and the need for Parliament Subject Committees to complete their pre-Budget scrutiny.
“I look forward to working with the Finance Committee and the Parliament to secure a Budget that will work for Scotland.”