A double-entry Schengen visa allows travelers to stay in the Schengen Area for a maximum of 90 days within a 180-day period, per entry. However, this limit isn't always set at the maximum. In some cases, the visa may be issued for a shorter duration. For example, you might receive a double-entry visa with a permitted stay of up to 10 days. In this case, the total number of days you can spend in the Schengen Area—across both entries—is 10 days, not 10 days per entry.
The key point to remember is that the 90-day limit applies to the overall time spent within the Schengen Area across all countries visited during your stay. It doesn’t reset for each Schengen country you enter. If you visit multiple Schengen countries during a single entry, the combined time spent in all those countries cannot exceed the allowed duration of your visa.
For travelers who need to stay in the Schengen Area for longer than 90 days, a long-stay visa or residence permit may be required, depending on the purpose of your extended stay.
If you're planning to travel to the Schengen Area, make sure to calculate the total number of days you intend to spend in all Schengen countries during both entries, to avoid overstaying your visa and facing penalties or restrictions on future travel.