Stuck in MS Project? A Guide to Safely Changing Project Dates

Microsoft Project is an incredibly powerful tool for project management, but it can also be frustrating, especially when it comes to dates. One of the most common problems new users face is trying to change a task's date, only to have MS Project seemingly ignore the change or move it back. This happens because Project is a scheduling engine, not a simple spreadsheet. This guide will explain why you can't just type in a new date and show you the correct, safe way to change your project schedule.

The Core Problem: Task Dependencies and Constraints

The reason you can't just change a date is that MS Project schedules tasks based on a set of rules. The start date of a task is determined by its relationships to other tasks, not by a date you manually enter. Think of it like a chain: the start of one link is dependent on the end of the previous link.

The Wrong Way: Manually Changing Dates

If you go into the "Start" or "Finish" column and manually type in a date for a task, you are creating what's called a constraint . You are telling Project, "This task MUST start on this date, no matter what." This breaks the dynamic nature of your schedule. A small calendar icon will appear in the task indicator column, signifying a constraint has been placed. While this seems to work at first, it creates major problems down the line when you need to adjust the schedule, as the constrained task will not move automatically with its predecessors.

The Right Way: Adjusting the Project's Logic

To safely change your project's dates, you need to work *with* the scheduling engine, not against it. This means adjusting the inputs that Project uses to calculate the dates for you.

Method 1: Adjust the Project Start Date

If your entire project needs to be shifted, the safest and easiest way is to move the project's overall start date.

Go to the Project tab on the ribbon.
Click on Project Information .
In the dialog box, change the Start date to your new desired start date.
Click OK.

MS Project will then automatically recalculate the dates for every single task in your project, shifting the entire schedule forward or backward while preserving all the dependencies you have built.

Method 2: Adjust Task Durations

If a specific task is starting too early, it might be because the duration of a task that comes before it (a "predecessor") is too short. Instead of changing the start date of the later task, correct the duration of the earlier one.

Example: If "Task B" starts on Wednesday but you need it to start on Friday, and it is dependent on "Task A," check the duration of Task A. If Task A only has a 1-day duration, perhaps it really needs 3 days. By changing Task A's duration from 1 to 3, MS Project will automatically push the start date of Task B to Friday.

Method 3: Adjust Task Dependencies

This is the most common and powerful method. The relationships between your tasks dictate the schedule. Make sure they are correct.

Finish-to-Start (FS): The most common type. Task B cannot start until Task A is finished.
Start-to-Start (SS): Task B cannot start until Task A starts.
Finish-to-Finish (FF): Task B cannot finish until Task A finishes.

If a task date is wrong, check its predecessors in the Predecessors column. Is the relationship correct? Should it be linked to a different task? Correcting the dependency is the proper way to adjust the schedule.

Method 4: Use Lag or Lead Time

What if there's a required delay between two tasks? For example, after you pour concrete (Task A), you have to wait 3 days for it to cure before you can start framing walls (Task B). You don't want to just manually set the date for Task B. Instead, you use "lag."

How: In the Predecessors column for Task B, you would enter the predecessor task number followed by the lag. For example, if Task A is task number 5, you would enter 5FS+3d . This tells Project that Task B can start 3 days AFTER Task 5 finishes.

What If You Absolutely MUST Fix a Date?

Sometimes, you have a hard deadline or a fixed event date that is not dependent on other tasks (e.g., a trade show on a specific date). In this case, and only this case, it is appropriate to use a constraint.

Double-click on the task to open the Task Information dialog box.
Go to the Advanced tab.
Use the "Constraint type" dropdown menu to select a constraint like "Must Start On" or "Finish No Later Than."
Enter the date in the "Constraint date" field.

Use constraints sparingly. A project plan littered with manual constraints is a sign of a poorly constructed schedule and will be a nightmare to manage when delays occur.

Conclusion: Let the Engine Do the Work

The key to mastering MS Project is to stop thinking of it as a spreadsheet where you enter dates. It is a dynamic scheduling engine. Your job is to feed it the correct logic—the project start date, the task durations, and the dependencies between tasks. If you provide the correct logic, the engine will calculate the correct dates for you. When you need to make a change, don't force a date; instead, adjust the logic that led to that date. This approach will make your project plan more robust, flexible, and ultimately, more accurate.

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