Iberia and Turkish Airlines share the MAD-IST corridor; 3 h 45 min eastbound with a.
The eastbound leg enjoys a slight tailwind, trimming the flight to about 3 h 45 min versus 4 hours westbound. Turkish Airlines is the dominant carrier with daily nonstops. Iberia has added MAD-IST service reflecting growing Spain-Turkey tourism demand. Both depart from T4S at MAD. Madrid - Istanbul timing usually sits around ~3 h 45 min eastbound, so departure windows matter.
Spanish passport holders need a Turkish e-Visa ($50, valid 90 days). Apply at evisa.gov.tr -- approval is instant in most cases. Istanbul Airport (IST) is massive; allow 20 minutes to walk from aircraft to immigration. The Havaist bus reaches Taksim in 40-50 minutes. On Madrid - Istanbul, compare airport pair MAD -> IST and total trip cost before paying.
Spanish school holidays (Semana Santa in April, summer in July-August, and Christmas) drive MAD-IST demand. February-March and late October to mid-November offer the softest pricing. Turkish Airlines often includes Istanbul stopover packages for transit passengers. Madrid to Istanbul fares move quickly, so flexible date checks usually save money.
Yes. A Turkish e-Visa is required ($50). Apply at evisa. gov.
Turkish Airlines has more daily frequencies and the IST hub lounge advantage. Iberia is convenient for Avios-collecting travellers and connects well from other Spanish cities via MAD. Pricing is similar on most dates.
Havaist bus to Taksim takes 40-50 minutes for TRY 140. Metro M11 connects to the city network. Taxis cost TRY 400-500 to central Istanbul depending on traffic.