In this calculator, a time interval can be displayed as a percentage of another time interval. Both time intervals can be entered in days and time. By default the calculator shows the percentage time elapsed in the current day.
The reverse interpretation of the fraction as time can also be convenient. Suppose you need to imagine the relation of some time period to a whole time scale (e.g. 200 years of industrial age to 6000 years of the entire duration of human civilization).
In fact, this calculator was inspired by the Time period as minutes to midnight work. I spent some time understanding its concept, and when I figured it out, I decided to implement a simple analogue of it.