# Calculate start date based off of end date

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Hi All,

Can someone help me with a formula? I've searched the community and haven't been able to find an answer. I already have a formula in place to calculate the end date based off of the start date and duration of project. However, if I have an already defined end date I'd like to calculate the start date based off of the pre-defined end date and duration of project.

Use Case: non-negotiable end date of July 1, 2024. Project is 10 weeks long. What date should the project begin to meet that end date?

Thank you all for your help!

Tammy Sutton, CSM, CSPO

Project Manager | MilkTracker

AngelEye Health

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Thank you @heyjay I appreciate your answer. That will get me a date for just a single cell. I'm wondering about a more automated date that I can make a column formula based off of end date - duration = start date.

Tammy Sutton, CSM, CSPO

Project Manager | MilkTracker

AngelEye Health

• ✭✭✭✭

Ohhhh, I just learned that with the current dependency setup. If I put in the start date and the duration it configures the end date. BUT.....if instead of putting in the start date I put in end date and the same duration it works backwards. SIGH, should have tried that prior to posting my question.

Thanks all!

Tammy Sutton, CSM, CSPO

Project Manager | MilkTracker

AngelEye Health

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```=date(2024,7,1) - 70
```

70 is 10weeks x 7days (in a week). You can replace the date function is you have a reference cell.

`date@row`

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• ✭✭✭✭

Thank you @heyjay I appreciate your answer. That will get me a date for just a single cell. I'm wondering about a more automated date that I can make a column formula based off of end date - duration = start date.

Tammy Sutton, CSM, CSPO

Project Manager | MilkTracker

AngelEye Health

• ✭✭✭✭✭
```=[End Date]@row - Duration@row
```

...

• ✭✭✭✭

Ohhhh, I just learned that with the current dependency setup. If I put in the start date and the duration it configures the end date. BUT.....if instead of putting in the start date I put in end date and the same duration it works backwards. SIGH, should have tried that prior to posting my question.

Thanks all!

Tammy Sutton, CSM, CSPO

Project Manager | MilkTracker

AngelEye Health