Instead of Calibri, the Microsoft-provided typeface to use for mathematics is Cambria, https://en.wikipedia.org/wiki/Cambria_(typeface)#Cambria_Mat...
Personally I like Minion, http://www.typoma.com/en/fonts.html
Or combining some kind of Renaissance-style typeface with AMS Euler https://en.wikipedia.org/wiki/AMS_Euler
Or Lucida Math, https://tug.org/store/lucida/opentype.html
If you prefer Times, try MathTime https://en.wikipedia.org/wiki/MathTime TM Math http://www.micropress-inc.com/fonts/tmmath/tmmain.htm or STIX https://en.wikipedia.org/wiki/STIX_Fonts_project