After how many days do you start to calculate the fat loss?

In the first 24-48(?) days you just use your glycogen, so what is the estimated time to start calculating the fat loss? Let's assume I do 5 days fast. Height 1.78m, weight 87kg.

Answer

You want consistency throughout a long period of time.

I weigh myself once a week on Monday. I do it at the same time and I do it completely naked. I think that’s the best way to get an accurate representation of how you’re progressing.

Answer

I just times my maintenance by the number of days I fasted and divide by 3500. I take that value with a grain of salt and realize my actual fat loss is less than that. But I don’t care about it being precise. I just like having a rough idea of how much I loss. It’ll sort itself out a few days after my fast when I weigh myself.