Supposedly you learned the basics of Calculus and Differential Equations in your undergraduate classics. Have you perhaps forgotten some of it? Or did you try to ignore differential equations classes, in hopes they would perhaps go away? You might be interested in
If you remember most of the ideas, but need to refresh your memory about formulas, check out a book of math tables.
See the page on numerical analysis for algorithms to compute derivatives or integrals, solve differential equations, and the like.