Need to classify expenses based on when were incurred

Please some help here:

This is how my table looks like. I would like to classify each amount into the corresponding week using starting date of 01/15/2019. I will use this template for different projects so starting date will vary from one project to another.

Date Amount Week 1 Week 2 Week 3 Total
2/3/2019 200
2/5/2019 250
2/9/2019 350
2/11/2019 258
2/18/2019 900
3/5/2019 280


Total $- $- $- $- $- $- $-

So if I incurred in expenses 7 days after my starting date (01/15/2019 in this case) I would like those 200 to appear in the Week 3 (01/15/2019 +7 days would be first column, 01/15/2019 +14 days would be in week 2 column, 01/15/2019 +21 days would be Week 3 column and so on).
Not sure if Im explaining my self clearly, but I would like to know a total spent by week based on the starting date and when the expense was incurred and bring that amount to the correct week in order to totalize it by week.

Thanks!!!!

Reference date = 01/05/2019 - you could have this as a named range, a today() formaula, or a cell eg. 1A

Formula for:
Week 1 =IF((reference date - row date)<=7,row amount,0)
Week 2 =IF((reference date - row date)<=14,row amount-Week1,0)
Week 3 =IF((reference date - row date)<=21,row amount-Week1-Week2,0)