even on 19th eve there will be 10's of poll and all will vary between 215 - 300 and yet final answer will be known only on 23rd. However, mean/avg of exit poll could give us fair idea.
My personal calculations based on UP voting in 2014 suggests bjp wining just 43 seats (in 2014 they won 71, lost 1 in bypolls later so 70). This was based on SP+BSP fighting together. I gave benefit of doubt to BJP on all seats with 40% vote even if 43% were towards SP+BSP and yet it didn't crossed 50 mark.
It's expected that bjp will lose few seats in gujarat/mp/rajasthan and chattisgarh too but not at the scale of UP as rest places there is no major threat to bjp.
Also, consider that in 2014 bjp won on 282 seats, but couldn't win a single by-election and lost 10 parliament seats even though Modi lahar was in place.
so 271 - 25/30 seat lose in UP - some other losses gives around 220/230 seats to bjp, which means NDA will form govt but will need Biju Patnayak + Mamta and/or TDP back in NDA. In worst case along with Didi, Bahanji could back BJP govt too. It happened in past even after 'tilak taraju aur talwar.. inko jute maro chaar' bjp + bsp formed govt in UP not once but twice.. Mahathagbandhan, Mahamilawat or tukade-tukade gang is real possibility whether it's Congress or BJP.