Bulgaria to join euro area on 1 January 2026

This will likely come with a one-time significant increase in inflation, at least based on other European countries.

When Germany converted to the Euro, the conversion rate was (IIRC) about ~2 DM to the Euro but from what I recall, a lot of everyday things went from costing 7 DM to 7 euro, effectively doubling in price. IIRC France was similar (ie ~6.5 francs to the Euro but 10 Francs went to 3 euro, etc).

I've tried searching for any studies on this to see if the effect was measured and, if so, whether it held with later countries joining the euro.

I'm a little surprised that the euro has been this stable for this long (going on 30 years). Finland debated leaving. IT's debated if there's even a legal mechanism to leave. We still have the problem that the ECB sets eurozone monetary policy with Germany and Greece being vastly different economies.

The Euro expansion is the mechanism the EU has to export inflation to other countries, similar to the way the US exports inflation with dollar trading across the world. When the easy expansion stops, this is when the debasement will start to occur. The US is already at this point, very soon the dollar will be less valuable as less trading is happening in USD.

I think there are other motives otherwise Bulgaria would say, no thank you. IMHO, the primary motivation is to establish/strengthen the single market and the economic cohesion of the EU. That inflation is a side effect of this (and part of the stabilization) might be the case.