Microsoft Word has a date field, but it's not easy to use in an expression. If you need to update dates in a document, use Excel to calculate the dates and then run a mail merge.

Click Insert Merge Field in the Write & Insert Fields group and choose M_1st_First_Name field from the resulting list (Figure H). This dropdown lists all the fields from the Excel sheet.

Click the Insert Merge Fields button in the Mail Merge toolbar. Click Attendee_Name, Insert, and then Close. Click the Merge To Printer button.

In Microsoft Word, you can insert built-in or custom fields into your Word document that may change within your document. Learn how to insert a Text field in Word.

Then in your message, position your cursor where you want the balance due to display, click the Insert Merge Field button from the Write & Insert Fields group, and select Other from the dropdown menu.