Kenny Jackett has set an 85-point promotion target.
The Pompey boss is anticipating it will be a high total to reach the Championship through the automatic berths this season.
And Jackett believes it will take around 75 points to make it to the play-offs.
His side currently sit on 59 points with 15 games remaining of the campaign.
The Blues boss has made it clear he believes a ‘sprint finish’ is going to be needed to finish in the top two, with Luton’s storming form seeing them break clear of the pack.
That may not quite hit the unusually high totals of last term when Shrewsbury finished third on 87 points, behind Blackburn (96 points) and champions Wigan (98 points).
Jackett can see it matching the 2015-16 and 2016-17 seasons when 85 and 86 points respectively was the return needed to make the top two.
He said: ‘They’re high numbers. It’s going to be high.
‘They’ll be two sides who keep going and do very well - there’s no doubt about that.
‘Last year Shrewsbury got 87 and finished third.
‘Whether it will be quiet as high as that again, I don’t know, but it will certainly be high.
‘You’re probably looking at 85 plus.’
Pompey finished on 66 points last season on their return to League One - which was five points shy of the total required to make the top six.
Jackett feels it could be heading for an unusually high return of 75 points for the play-offs.
The last time it was that high was when Huddersfield finished sixth on 80 points in 2010.
Jackett added: ‘You will need 70-75 points and I suggest it will be more 75 points for the play-offs.’