Simplifying a LINQ expression that finds the largest date smaller than another date
Is this what you are looking for?

skew.CalibrationDate.Date == db.Skew
    .Where(s =&gt; s.CalibrationDate.Date &lt;= date.Date)
    .Max(s =&gt; s.CalibrationDate.Date)


Max will return the maximum value itself, not the object with the maximum date.