The Baggies suffered a 3-0 defat to Leicester City, ending a two match winning streak.
They are now nine points from safety with just six games remaining.
"We are going to need five wins from six to be absolutely certain," Allardyce said, with his team set to play Aston Villa on Sunday.
"That would take us to 39 points which normally does it.
"Is four from six going to be enough? Maybe not.
"Leicester were far too good for us, in the first half particularly.
"We tried to look after their front two and one of the main reasons for our recent results has been our defensive solidarity.
"But Leicester tore it apart. We couldn't cope with them.
"We had a good chance to open the scoring but Mbaye Diagne missed his kick and those are the sort of chances we can't afford to miss.
"In the end, we thoroughly deserved to get beat.
"Was it great pressure from Leicester that forced us into so many errors? They are on a high, you can see why they are in the top four, they are as good as anyone in the league apart from Manchester City.
"You have to get the basics right and those basics deserted us."