When sending payments, Dutch bank Bunq has basic calculator functionality which allows simple calculations to be performed.
Here’s a video of the calculator in action:
I think an inbuilt calculator would be really useful for sending payments and calculating Bill Splits since it would reduce the need to switch between the Monzo app and a calculator app when figuring out values.
NB: to save space when using the calculator in Bill Splits, the calculation could appear in a bar just above the operator symbols instead of above the result of the calculation.
If you mean switching between apps, having a built-in calculator would make the process of calculating payments or splits much easier and be a nicer UX.
I signed up to the forum to request/vote up this feature. It would be useful for more than bill splitting alone. I would find it particularly useful for multi-category transactions. I have separate food and household categories that often end up on the same supermarket receipt. Being able to do inline calculations to sum up the household items right there inside the numerical field would be breezy.