The French government faces a 14bn-euro black hole in its public finances after overestimating tax income for the last financial year.
French President Francois Hollande has raised income tax, VAT and corporation tax since he was elected two years ago.
The Court of Auditors said receipts from all three taxes amounted to an extra 16bn euros in 2013.
That was a little more than half the government’s forecast of 30bn euros of extra tax income.
The Court of Auditors, which oversees the government’s accounts, said the Elysee Palace’s forecasts of tax revenue in 2013 were so wildly inaccurate that they cast doubt on its forecasts for this year.
It added the forecasts were overly optimistic and based on inaccurate projections.