Growth speed fertilizer math

[Thorinair]

I found a math issue related to growth speed fertilizers.

An example of this issue is visible when planting Ancient Fruit with Deluxe Speed-Gro. Say that you plant the seeds in 1st of any month. The website will say that the first batch will grow on 22nd, which is incorrect. The seeds will actually grow on 23rd (I checked ingame), so I suspect some sort of a rounding error.

I haven't tried combinations of other crops and fertilizers however.