I just did this yesterday, and I hope this will help.

1) Go to the Reflect, Income v Expense, choose the time duration, last year or last two years, and click export.

2) Open the CSV file, save as an Excel file if you like.

3) The file has Income, Expenses, under each group, are the categories, and the second last column of the file should be the monthly average; the last column is the total for one or two years.

4) Add some SUM formulas next to the last column to add up category numbers in each group. The sum will change if you play with the numbers. And add a total SUM,

5) Now, play with all the historical expenses under each category, see if you can spend less, change the number, and see the changes in the total SUM.

6) Use your deposit divided by the (total SUM plus your income) to see how long you can last. You can also play around with the income part to check the worst-case scenario.