If you want to save money traveling from Delhi to Kolkata, you can take the train and be there overnight in less than 18 hours. Find out about the best trains from Delhi to Kolkata here.

The main railway station in Delhi is New Delhi Railway Station (NDLS), near Paharganj.
Trains from Delhi arrive at both Howrah Junction (HWH) and Sealdah (SDAH) railways stations in Kolkata. Howrah station is located a short distance north of the city center, on the other side of the Howrah Bridge, across the Hooghly River. Sealdah station is located a little east of the city center.
Delhi Kolkata Trains

The fastest train from Delhi to Kolkata is the newly introduced 2260 Sealdah-New Delhi Duronto. This train only runs on Mondays and Fridays though. It departs from New Delhi Railway Station at 8.05 p.m. and arrives at Sealdah the next day 12.25 p.m. The fare for in 1AC (first class, air conditioned, sleeper) is 3,295 rupees. 2AC (two tier, air conditioned, sleeper) is 1,880 rupees. 3AC (three tier, air conditioned, sleeper) is 1,390 rupees.
Also very fast is the premium 2302 Kolkata Rajdhani service. It departs New Delhi Railway Station at 5.00 p.m. and arrives at Howrah Jn at 9.55 a.m. the next morning. The fare in 1AC is 3,365 rupees. 2AC is 2,010 rupees. 3AC is 1,520 rupees. The train runs every day except Fridays, and meals are included.
The premium 2314 Sealdah Rajdhani from New Delhi Railway Station to Sealdah is another fast option. It departs at 4.30 p.m. and arrives at 10.15 a.m. the next morning. The fares are the same as the Mumbai Rajdhani train. The train runs every day, and meals are included.
Another relatively convenient option is the 2304 Poorva Express superfast train. This train departs New Delhi Railway Station at 4.30 p.m. and arrives at Howrah at 4.45 p.m. the next day. The fare in 1AC is 2,743 rupees. 2AC is 1,623 rupees. 3AC is 1,187 rupees. SL (non air conditioned sleeper) is 442 rupees. The train only runs on Wednesdays, Thursdays, Saturdays, and Sundays.
A slightly faster option is the 2330 WB SMPRK Kranti, although it's not as convenient. The train leaves from Delhi station (near Chandni Chowk in Old Delhi) and only runs on Tuesdays and Saturdays. It's departure time from Delhi is 7.10 p.m. and arrives at Sealdah the next afternoon at 5.25 p.m. The fare in 2AC is 1,561 rupees. 3AC is 1,143 rupees. SL (non air conditioned sleeper) is 462 rupees.