To facilitate the introduction of a single currency in Economic Community of West African States (ECOWAS), the fiscal convergence criterion currently proposed by countries limits the public deficit to 3 per cent of GDP. According to the literature, the limitation of the public deficit to a given threshold is the most fundamental norm of the various convergence pacts existing and needed for monetary integration. Through a nonlinear panel data model, this paper tests the validity of the threshold by determining the public deficit threshold not to be exceeded so that fiscal policy has a positive effect on economic growth. Over the decade 2007-2016, this threshold is estimated at 4.74 per cent of GDP. Thus, the paper concludes that the proposed convergence criterion of 3 per cent of GDP is pro-growth. However, in relation to the estimated threshold, there is a room for manoeuvre that can be used for supporting economic growth. Thus, the proposed threshold could be readjusted upward. The analysis also reveals that only four countries in ECOWAS are on the track to respect in the future, the proposed fiscal criterion and therefore are taking an important step toward the adoption of the future currency. The other countries need to make significant fiscal consolidation operations before hoping to adopt the single currency on the basis of fiscal discipline.