A 13-Week Cash Flow Forecast in Google Sheets: Weekly Buckets and a Running Balance

A 13-week cash flow forecast is a rolling view of money in and money out, broken into weekly buckets instead of monthly ones. Freelancers and small operators use it because a month is too coarse to catch a week where three invoices are late and a tax payment lands on the same Friday. The spreadsheet mechanics are just date bucketing, SUMIFS, and a running balance. Here’s how to build it.

Sheet structure

Use two tabs. Transactions holds every actual and projected cash movement:

Type is either “Income” or “Expense”, entered as a positive number regardless of direction. Keeping the sign out of the amount column avoids double-negative bugs later when you sum things.

The Forecast tab has 13 columns, one per week, with a date in row 1 marking each week’s start:

        B1          C1          D1     ...
Week    8/17/2026   8/24/2026   8/31/2026

Each subsequent week’s header is just the prior one plus 7:

=B1+7

Bucketing transactions into weeks

Row 3 pulls total income for each week by matching the transaction date against that week’s start and the following week’s start:

=SUMIFS(Transactions!$D:$D, Transactions!$C:$C, "Income", Transactions!$A:$A, ">="&B$1, Transactions!$A:$A, "<"&B$1+7)

Row 4 does the same for expenses, changing only the type:

=SUMIFS(Transactions!$D:$D, Transactions!$C:$C, "Expense", Transactions!$A:$A, ">="&B$1, Transactions!$A:$A, "<"&B$1+7)

Copy both formulas across all 13 columns. Because the date bounds reference B$1 relatively (column shifts, row stays fixed) and the ranges reference Transactions! absolutely, each column automatically pulls its own week without any manual editing.

Net change for the week is row 3 minus row 4:

=B3-B4

The running balance

This is the part that makes the forecast useful instead of just a chart of weekly totals. Put a starting cash balance in a fixed cell, say A2, then build the ending balance row so each week’s ending balance feeds into the next week’s beginning balance.

Beginning balance for week 1:

=A2

Beginning balance for week 2 onward (in cell C6, referencing week 1’s ending balance in B7):

=B7

Ending balance for each week:

=B6+B5

Where row 6 is beginning balance and row 5 is net change. Drag both rows across, and the balance rolls forward automatically. If income in week 4 comes in light, every week after it shows the drop without you touching a single cell.

Finding the tightest week

Once the running balance row is built, MIN tells you the lowest point in the 13-week window:

=MIN(B7:N7)

To find which week that low point falls on, pair INDEX with MATCH against the header row:

=INDEX(B1:N1, MATCH(MIN(B7:N7), B7:N7, 0))

That returns the date of the week where the balance bottoms out, which is more useful than the number alone when you’re scanning the sheet quickly.

Adding a forecast-vs-actual check

If you’re logging both projected and actual transactions, add a Status column to Transactions (“Forecast” or “Actual”) and split the SUMIFS with an extra criteria pair:

=SUMIFS(Transactions!$D:$D, Transactions!$C:$C, "Income", Transactions!$B:$B, "Actual", Transactions!$A:$A, ">="&B$1, Transactions!$A:$A, "<"&B$1+7)

Subtracting this from the all-status total for the same week gives you the outstanding forecasted amount still expected to land, which is handy for spotting weeks that are more guess than fact.

Keeping it rolling

To keep the sheet at 13 weeks as time passes, don’t hardcode 13 static columns forever. Once week 1 closes, delete that column and add a new week 13 at the end with a header formula referencing the prior week plus 7. The running balance formulas don’t need to change since they reference the row above them, not a fixed starting column. The only manual step is dropping in the new week’s header date and copying the SUMIFS formulas one column to the right.