calculator.exe is a application which is most likely NOT a virus or malware. So, if calculator.exe is on your PC, it is most likely ok, and will NOT cause problems. Even if your PC is clean, it is still recommended to run a good antivirus with a good track record, in order to defend yourself against threats.
Usually, this program is stored in C:\Program Files\WindowsApps\Microsoft.WindowsCalculator_10.1712.3351.0_x86__8wekyb3d8bbwe\Calculator.exe.
The MD5 checksum for this file is ee122a6c9c2bc5e43697c5dc476430da.
This program does NOT operate as a Windows service. This is usually a good sign.
This program runs in 32-bit mode. It can not use the entire set of features of current computer processors. This is quite normal because the makers did not upgrade it to 64-bit code.
calculator.exe appears to have a visible user interface. This means it doesn't work in a kind of invisible mode. Its activity is clearly displayed to you.
The digital signature is missing from this program. The authors did not sign it. This is usually bad.
This program does NOT have an uninstall routine set up in registry.