Latest tax figures show the State collected slightly more tax than it expected last month.
However, the Department of Finance said all categories of taxation will have to perform strongly in the next two months if it is to fund its spending of €56bn.
The Exchequer returns for the month of October show taxes were 4% higher than forecast.
It means the Government is also 1.7% ahead of its projection for the first ten months of the year.
The amount of Value Added Tax collected so far this year is 2.6% behind expectations.
Officials believe this weakness is being caused by lower than expected inflation.
Latest inflation figures show the price of goods and services have not increased over the past 12 months in contrast to the department's forecast of a 1.1% rise.
So far the tax figures show no hard evidence of the first effects of Brexit.
The Department of Finance said in a note: "In relation to the revised tax revenue forecast of €48.1bn (additional €900m) we are still on track to achieve this target.
"However, it will require all tax-heads to perform strongly in the last two months."
It said the achievement of this target is necessary to fund the expenditure of €56bn projected for 2016.
It said this target was €850m higher than originally published in the Revised Estimates as it includes an additional €500m for the Department of Health and €40m for the Department of Justice.
There was also a further €310m to fund the Christmas Bonus for long-term social welfare recipients, for increased capital expenditure on the school building programme and for flood repairs to transport infrastructure.