How hard is it to double major at Yale in two completely different fields, e.g. biology and econ/finance/math?
It’s definitely very doable, though you won’t have the freedom to take as many courses in other fields that you may fancy, like history or CS.
A senior needs at least 36 course credits to graduate. The Econ and CS majors for instance (not too familiar with Bio requirements) need about 12 course credits each. Add to this number a few more courses to satisfy the prerequisites and you’re left with about 5-8 ‘free’ choices. Note that you’ll also have to satisfy a couple of other distributional requirements that you may have missed out through these remaining course credits, like the foreign language requirement.
Agree that it’s very doable. However, not too sure it makes sense career wise unless you want to do public health or something similar - most of the economics related jobs are accessible to biology majors, and med school is also accessible without a biology major.