Upvote:2
The rule is that within any 180 days time windows, you must not be present in the Schengen zone for more than 90 calendar days. It does not matter when it is "half time" - if there is any period of 180 consecutive days in which you would be present for 91 days or more, you would overstay your visa.
The EU has a Schengen visa calculator that allows you to check if your plans are OK here:
Note that your visa may also have a limit on the overall number of days spent in the Schengen area, which you must take in consideration in addition to the 90/180 rule.