Sum by week

=SUMIFS(value,date,">="&A1,date,"<"&A1+7)
To sum by week, you can use a formula based on the SUMIFS function. In the example shown, the formula in F4 is:
=SUMIFS(amount,date,">="&E4,date,"<"&E4+7)
This formula uses the named ranges "amount" (C4:C21) and "date" (B4:B21).
The SUMIFS function can sum ranges based on multiple criteria.
In this problem, we configure SUMIFS to sum amounts by week using two criteria: (1) dates greater than or equal to the date in column E, (2) dates less than the date in column E plus 7 days:
=SUMIFS(amount,date,">="&E4,date,"<"&E4+7)
When this formula is copied down, SUMIFS generates a sum for each week.
The dates in column E are Mondays. The first date is hard-coded, and the rest of the Mondays are calculated with a simple formula:
=E4+7
Pivot Table solution
A pivot table is an excellent solution when you need to summarize data by year, month, quarter, and so on, because they will do this kind of grouping for you without any formulas at all. For a side-by-side comparison of formulas vs. pivot tables, see this video: Why pivot tables.
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