Handelsblatt newspaper reported on Wednesday that the economists estimate next year's budget will sport a €3.5 billion hole.
“If the government has to refund its nuclear fuel tax again, the gap would be that much bigger,” IfW expert Alfred Boss told the business newspaper.
MPs are debating the 2015 budget in the Bundestag this week. The annual "General Debate" will be held on the floor of parliament on Wednesday morning.
This important moment in the political calendar traditionally sees opposition politicians attacking the government's forecasts.
Politicians will observe a "memorial hour", including a speech by Polish President Bronislaw Komorowski, before the debate begins to commemorate the 75th anniversary of the outbreak of the Second World War.
The problems with restraining the government budget might even begin this year, as Boss estimates that the 2014 budget deficit will reach €7.7 billion, or €1.2 billion more than Schäuble had planned for.
Some coalition allies reportedly believe the Finance Minister might overshoot his budget by €1.5 billion, prompting them to begin combing through the budget to find potential savings.
The Bundesbank confirmed that the 2014 budget was “much more tightly forecast than in previous years".
Schäuble's plan forecasts income and expenditure of €299.5 billion for the coming year – the first time since 1970 since the state has expected to balance the budget.
A year with no budget deficit would be Schäuble's crowning achievement as Finance Minister, next to keeping the Eurozone together.
A survey from the Pew Research Center released on Tuesday showed Germans remained optimistic about their country's economy. The survey showed 85 percent of people were optimistic about the German economy in Spring 2014, up from 75 percent a year ago.
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