(Adds details, context)
BRASILIA, Jan 29 (Reuters) - Brazil's central government easily met its 2017 primary budget deficit target after rising tax revenue led to a smaller-than-expected December shortfall, in a boost to President Michel Temer's austerity credentials.
The central government, comprised of the federal government, social security system and the central bank, posted a deficit of 124.401 billion reais ($39.3 billion) in 2017 before interest rate payments, down 23 percent from the year before, government data showed on Monday.
The official target was 159 billion reais.
Reuters had reported last week that the deficit was likely to be around 30 billion reais smaller than the official target.
The December deficit totaled 21.168 billion reais, below the median estimate of 25.2 billion reais in a Reuters poll.
Brazil's economic recovery from its deepest recession in decades has lifted tax collecting above forecasts, cutting the government some slack as its struggle to cut government spending.
Still, it was the fourth straight annual primary deficit, highlighting the challenges facing policymakers as they try to curb growth of public debt in the wake of a sovereign downgrade.
($1 = 3.17 reais) (Reporting by Marcela Ayres; Writing by Bruno Federowski; Editing by Andrea Ricci)