The European Union's poorest member ended 2014 with a fiscal shortfall worth 3.7 percent of GDP, partly due to political instability and the collapse of the country's fourth-largest lender, Corporate Commercial Bank.
At the end of January the fiscal surplus stood at 69 million levs ($40 million) or 0.1 percent of GDP, the finance ministry said, the first surplus for the month of January since 2009.
The ministry said it expected the country to return to a small deficit by the end of February, although it expects the shortfall to be smaller than it was at the same point last year.
Revenue in January jumped 19.3 percent to 2.5 billion levs compared with the same month last year, while spending dropped 1.7 percent to 2.4 billion levs, data showed.
The centre-right government of Prime Minister Boiko Borisov that came to power in November has pledged to tighten up on tax collection.
The fiscal reserves the country is obliged to keep as part of its currency regime pegging the lev to the euro stood at 7.1 billion levs at the end of January, compared with 9.2 billion a month earlier.
Sofia must keep fiscal policy tight to protect the currency peg. The country operates a currency board system under which the central bank is prevented from setting interest rates, leaving fiscal policy as the key tool for influencing the economy.
The government expects the Bulgarian economy to grow 0.8 percent this year, down from an estimated 1.5 percent expansion in 2014.