I used excel to track weight, calories, and the theoretical surplus. Then I used the rough estimate of 3500 surplus calories for a pound of weight gain. So that’s red line.
After a couple months I could see some trends and added another line that adjusted my surplus each day as my metabolic rate increased.
Using speed of weight gain I made rough guesses for the starting metabolism and speed of increase until it made a trend line that was similar to what was actually happening. So that’s the green line.
For me 6.5 seems to be the average I increase per day.
Overall it’s a very rough estimate… but maybe interesting to some!