Hoping this will be easy. I'm starting at 900 at need a field to go up one when an item is added to a list. Is there a simple formula to achieve this?
Thanks in advance
A workflow would be needed to take a number that you have and add 1 to it.
Here is an article I found that may help. http://gihanmaduranga.blogspot.com/2012/09/create-auto-increment-number-column-in.html or this http://www.sharepointdiary.com/2014/11/create-autonumber-column-in-sharepoint-list.html
I'll second Chris G that a workflow makes the most sense, however in the interest of variety you might be able to get away with using a calculated column based on the list ID number. Say the first item in the list is the one you want to be 900, you could calculate the column as ID (1) + 899. Then ID 2 (+899) would be 901, and so on.
Where this would run into problems is when you delete items from the list, it would create non-sequential items. SharePoint does not reuse ID numbers, so if you deleted ID 2 this column would go from 900 to 902 without a 901. A workflow could add logic to account for item deletion.
You can use default ID field which is auto incremental and add 900. If you are on SharePoint online, it would be easier to use Flow. You can hide the field so user don't see this in the new/edit form if needed. I have added the following expression in the MyID2 field.