You may not appreciate this, but Windows 10's own Calculator is already pretty comprehensive - tap on its hamburger menu and marvel at the scientific, programmer and units conversion modes. And this works on both phone and desktop. However, Calculator² (you've got to hate the non-standard alphabetic characters, which will come back to bite in months to come in applications links and lists) goes further, adding more of everything, plus comprehensive financial and currency calculation modules - at a small premium.

From the Store description:

Calculator² is the beautifully designed, all-in-one calculator app for students and professionals. The advanced scientific, financial and programmer calculators provide a comprehensive set of mathematical functions and constants to help you perform any type of calculation.

The currency converter, with exchange rates updated in real-time, and unit converter offer 150+ World currencies and over 200 units respectively, with customisable favourites to allow you to save conversions for easy reference.

Calculator² won't slow you down; the intuitive keyboard support allows you to simply type in functions to enter your calculations. 

Here's Calculator² in action:

Here it's being used in scientific and currency modes, with a comprehensive set of constants, functions and country options. Just type and calculate/convert...

There's even a binary mode, for programmers, something I've never seen before. Plus the usual Hexadecimal and various logic operations; (right) importantly, you can choose the way in which Calculator² works, i.e. specifying the function first and then the thing it operates on, or having a function operate on the number already 'up'. If that sounds confusing, just try out the two modes!

You can grab Calculator² UWP in the Store here. For either your phone or your laptop, etc. The two main money modes (financial calcs and currency conversions) are both behind the in-app-purchase, but it's only £1.70 (in the UK Store, at least), so it's a trivial donation to the developer to keep going and well worth it.