Mancini suggested before Christmas that he felt a team would need 90 points to secure the title, since when City have been held to a goalless draw at West Brom and seen their two-point lead at the top of the table wiped out.
City are now level with Manchester United with 45 points from 18 games, while Tottenham are seven points behind with a game in hand, and Mancini said: "It is difficult. In this moment City, United and Tottenham have a lot of points compared to other years."
He added: "If you said how many points you need to win the league, it is very difficult. I think you need to wait another six or eight games."
By way of comparison, United led the table with 38 points after 18 games last year, while Chelsea had 41 in December 2009.
City were frustrated at The Hawthorns on Boxing Day in a game they were expected to win comfortably, while United have wiped out a five-point deficit at the start of December - and narrowed the goal difference to five - with the aid of two successive 5-0 wins.
However, Mancini does not believe his team are feeling the pressure.
"I don't think this," he said. "We have taken 45 points and scored a lot of goals and we knew before West Brom it would be impossible to stay on the top (all the time) or to win the title in January.
"When you play against United, Tottenham or Chelsea, this is impossible. We should fight until the end and I think this championship will be decided in the last three or four games."
City have a tough January schedule starting with a trip to Sunderland on New Year's Day and a home clash with Liverpool two days later.