Microsoft has an official in-depth response to this question:
Considerations for server-side Automation of Office
They provide no support for automating Excel directly in the backend, and they recommend that you use various programming libraries for accessing and manipulating Excel documents directly.
Most server-side Automation tasks involve document creation or
editing. Office 2007 supports new Open XML file formats that let
developers create, edit, read, and transform file content on the
server side. These file formats use the System.IO.Package.IO namespace
in the Microsoft .NET 3.x Framework to edit Office files without using
the Office client applications themselves. This is the recommended and
supported method for handling changes to Office files from a service.
The Open XML file formats are a public standard.
You may be able to find a library for evaluating Excel formulas that works in your programming language of choice, or you could implement a basic one that supports the subset of functions you need for your business logic.