Greece\'s deputy finance minister on Monday said that international creditors had underestimated the impact of three years of austerity on the country\'s deep recession by using a faulty calculation. Christos Staikouras said the actual fiscal multiplier, or negative effect, of austerity on growth is \"around 1.0, not 0.5,\" the number used by auditors from the European Union, International Monetary Fund and the European Central Bank to draft their fiscal policy recommendations. As a result, the 49 billion euros ($64 billion) in cuts imposed by successive Greek governments since 2010 have failed to provide their forecast fiscal results, Staikouras told a conference organised by the International Herald Tribune. Greece\'s conservative-led government is in talks with the troika on an austerity package needed to unlock a loan payment of 31.5 billion euros. Athens had hoped to clinch an agreement with the auditors before a European Union summit on October 18 that is expected to discuss Greece. But Finance Minister Yannis Stournaras now says this is unlikely. \"We are trying, but I don\'t think so,\" he told reporters on Monday in relation to the chances of a deal before Thursday. \"The negotiations will continue until the summit and beyond,\" he said. The troika report on Greece is required by European leaders and the IMF before approval is given for the release of the funds. Another finance ministry source said that an emergency Eurogroup meeting between eurozone finance ministers on Greece was \"the most likely\" scenario to close the latest round of negotiations. Greece needs to secure the loan tranche by next month. The payment, which has been pending since June, is a part of the two rescue plans provided to the heavily-indebted eurozone country. Greece has also benefited from the cancellation of more than 100 billion euros in privately held debt. The government has presented a draft budget that foresees 7.8 billion in savings next year, but EU/IMF/ECB auditors say measures worth 9.2 billion are needed. The troika mission estimates that the Greek economy will contract by more than four percent in 2013, according to a finance ministry source, while the government expects gross domestic product to shrink by 3.8 percent.