Automatic date calculator in Excel

Office worker 175 Reputation points
2026-09-04T06:36:56.79+00:00

I have created a spreadsheet as shown below:

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This contains a number of project tasks, with the following information:

Project start date: Friday 5 June 2026.

Column A: Task list. Tasks over multiple days have start and end points.

Column C: Number of workdays since start date for each line item, excluding start date.

Column D: Calculated task deliverable date =WORKDAY($B$2,C3,$A$46:$A$59) where B2 = start date, C3 = number of workdays since start date and A46:A59 = holidays which are not to be included.

Column E: Workdays duration for tasks with a start and date (inclusive from start to end date).

e.g. E6=NETWORKDAYS(D5,D6,$A$46:$A$59), where D5 = Task 1 start date D6 = Task 1 end date, A46:A59 = holidays which are not to be included.

This information is based upon historical data and shows expected tasks and their duration. This information is then plugged in to another spreadsheet, where users can input a start date and all of the dates for each task will auto-populate, based upon the above data.

What I am seeking to do is find a method whereby the duration for any task within the spreadsheet can be modified by the user as required (e.g. F6) and a new task date is generated. When such a modification is carried out, the dates for subsequent tasks would also change according to their relationship to the precedent task, where there is a relationship between tasks/overlap.

What steps would I need to go through to do this? I can upload the spreadsheet to those who require it.

Many thanks!

Microsoft 365 and Office | Excel | For business | Windows
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  1. Teddie Dang 1,085 Reputation points Independent Advisor
    2026-09-04T08:08:52.3433333+00:00

    Hi @Office worker

    The general approach is to make each task date dependent on the previous task while keeping the Duration cell editable.

    For example, if your columns are:

    • A = Task
    • B = Duration (Days)
    • C = Start Date
    • D = Finish Date

    Use formulas such as:

    C3 = D2 + 1

    D3 = C3 + B3 - 1

    Then copy the formulas down for the remaining tasks.

    In the example below, changing Task 1 from 5 days to 10 days automatically updates its Finish Date and shifts the Start and Finish Dates of all subsequent tasks.

    User's image

    However, this approach assumes a simple finish-to-start dependency between tasks. If some tasks overlap or have more complex relationships, as shown in your example, you will need to define predecessor relationships and calculate dates from those dependencies rather than relying solely on the previous row.

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