The twice-annual report Thursday from a group of think tanks says the country will run a 7.7 billion-euro ($10.5 billion) surplus next year. They advise the government to take advantage by investing in infrastructure, education and research.
The institutes said the government should also try to fix so-called bracket creep, in which inflation pushes taxpayers into higher tax brackets.
The report trimmed the growth forecast for next year, to 1.8 percent from 1.9 percent in their last estimate in April. But they said the economy nevertheless remains strong, supported by increasing employment and a lessening of a debt crisis in other countries using the euro.