The single biggest controllable cost in a restaurant is wages, and the single biggest cause of wages drift is rostering on habit instead of revenue. “We always have three on the floor Tuesday” is not a roster.
The simple rule
Pick a wage% target for each day (it should be different for each day) and roster backwards from forecast revenue. Tuesday lunch and Saturday dinner have different shapes — one body too many on a Tuesday lunch costs you more in percentage terms than a body too few on a Saturday peak.
The forecast doesn’t have to be fancy
Last 4 weeks, same day of week, average. If your POS exports a weekly summary, you have everything you need. The first time you do this, expect to find at least one day a week running 4–6 percentage points over target.