Auto-Updating Formula to reflect YTD percentage

Hey Gang of Excel Gurus. Could not find the answer to this in search, probably because I don't know how to exactly describe the function I am looking for...

So I have a sales spreadsheet similar to the sample one attached here.

The question is how to create a formula to reflect a comparison sum that is a "rolling" total in column B (2025) so that I can compare as a Year to Date with Column C (2026).

In my example, I have sales numbers for this year, thus far. i want to know the percentage of what it was for the same period last year. I want the percentage to update so that when I eventually enter a value in for April, the sum for Jan-Apr in 2025 will update and thereby reflect the updated percentage in a different cell. Therefore: As of today the YTD percentage is....

Is there a way to do this? To have a formula update somehow when new data is entered in a different cell, or set of cells?