Kolkata
Everything leaves from one building. Netaji Subhas Chandra Bose International (CCU) runs a single integrated terminal, so there is no domestic-terminal guesswork before a CCU–DEL departure — check in, clear security, and your gate is in the same concourse whether you are on IndiGo, Air India, Akasa Air or SpiceJet. Delhi-bound departures cluster hard into the 06:00–10:00 business bank and again from 17:00, which is where fares firm up first. If you are booking inside a day or two, widen the search by an hour either side of the flight you want: on a sector with this much frequency, the seat one departure earlier is often meaningfully cheaper than the one you first clicked.