Decremental digits in SP list column when form is submitted

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Posted on by Charlie Martharper

943 Season of Giving Solutions 2025

Hi!

I have to do a reservation of spots and I am using a list (40 spots in total). I want to do a flow that when a form is submitted, it subtracts 1. So 39, 38... That would be showing in the form so everyone knows how many spots are still available.

How can I do it so every time a person submits a form, it creates an item and a column gives 1 digit less?

I dont know if I explained it so you can understand it.

The thing is I cant use power apps because I have to give external user permissions and I dont really know who will come so can give access previously. The unique way is using forms. The same happens with list in SP. So they will have to go to forms, see there how many free spots remain and reserve one when submit. Then next one who want to submit a form, will see 1 free spot less.

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Building flows

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Kalathiya 2,456 Super User 2026 Season 1 on at

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Hello @Charlie Martharper,

This is not possible with Microsoft Forms. Forms cannot update or modify an item (such as reducing a number in a list) each time someone submits a response. It also cannot display a live value like remaining spots inside the form.

A possible workaround is to use Power Automate with a SharePoint or Microsoft List. When a form is submitted, a flow can create a new item and update a column that tracks the remaining spots. If no spots are available, the flow can simply send an email to the user informing them that the spot is no longer available.

If this response resolves your issue, please mark it as the Verified Answer so it can help other community members as well.

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David_MA 14,956 Super User 2026 Season 1 on at

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When you say you will use forms, I assume you mean Microsoft Forms? If not, please specify the type of form you are using. If you are using Microsoft Forms, will the form be used one time only?

Also, it is unclear to me, why do you need this number and how will it be used? It seems like you want to show the result in the form, which is not possible if you are using Microsoft Forms. The closest that you can get to that with Microsoft Forms is to use a pre-filled URL Pre-populate fields in Microsoft Forms via URL parameter? | Microsoft Community Hub.

You could do this if you just need the number calculated for remaining seats:

Initialize an integer variable in your flow named open_seats and set it to 40.

Initialize another integer variable in your flow named baseline_id and set it to the last response ID before you are ready to go live. For example, 10.

When a new response is received, subtract basedline_id from the current response ID (11 would be the next one).

This will result in 1 (response_ID = 11 minus baseline_id = 10) = 1

Take this result, and subtract it from open_seats to return (open_seats = 40 - result = 1) = 39.

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