Weighted Formula for Months

[ZuneidDassu]

Hi I was hoping someone could help me, I have been trying to workout a weighted formula for the below but i have been struggling to come up with a solution.
I have an invoice from 16-Dec-17 to 02-Feb-18 over this 48 period the customer has used 100 units of energy. I wanted to know how I would workout how much energy he has used using a weighting scale factor. The weightings are as below.
The table below also shows number of days in the month and average energy usage.
Your help in this matter is much appreciated

16-Dec-17 02-Feb-18
Month Dec Jan Feb Total Days/energy
Days 15 31 2 48
Average 31 65 4 100
Energy

Jan 16%
Feb 14%
Mar 13%
Apr 9%
May 5%
Jun 3%
Jul 2%
Aug 2%
Sep 3%
Oct 7%
Nov 12%
Dec 15%

[Sam Capricci]

could you develop a sample workbook which represents the data you have AND expected results? That might be a help in developing a formula for your needs.