Who should do simple calculations: server or client?

The server should do calculations that require proper business logic, or that require information from multiple sources in order to generate a result.

The client should do all simple calculations, like adding together firstName and lastName.

If there's a chance two people could do the calculation and end up with different results, then the server should do this.

I am not including careless / simple mistakes in the category of different results. For example, if I forget to put in a space between first and last name, this is a careless / simple mistake. I should still do this calculation on the client. e.g.

let fullName = firstName + lastName // this is a simple mistake on the client
let fullName = firstName + " " + lastName // this is what I meant to do

I mean different results because we could reasonably interpret the logic in different ways. For example, legalName could or could not include middleName. Or perhaps depending on the locale, legalName might have the last name first, or the first name first.

In this scenario, two developers could reasonably interpret legalName differently, and so the server should generate this.