# Add/Subtract amounts from column in one list to "cell" in another list

I am trying to build two lists to keep track of our purchase orders we have. My two lists looks like this:

List 1: PO

``````+-----------+-----------+-------------+
| PO        | Amount    | Used/Left   |
+-----------+-----------+-------------+
| 654654654 |     50000 |          ?? |
| 123123123 |     30000 |          ?? |
| 789789789 |      5000 |          ?? |
+-----------+-----------+-------------+
``````

List 2: Purchases

``````+-----------+-----------+---------------+-----------+-----------+
| Supplier  | PO        | Description   | Amount    | Received  |
+-----------+-----------+---------------+-----------+-----------+
| Some name | 654654654 |     Blah blah | 1654      |    Yes/No |
| Some name | 123123123 |     Blah blah | 2441,41   |    Yes/No |
| Some name | 789789789 |     Blah blah | 154       |    Yes/No |
| Some name | 123123123 |     Blah blah | 4521,52   |    Yes/No |
| Some name | 789789789 |     Blah blah | 160       |    Yes/No |
+-----------+-----------+---------------+-----------+-----------+
``````

So here we go. In List 1 we have our PO's and the max usable amount and a column to the used amount. In List 2 we have the purchases made on the different PO's.

What I would like to accomplish is getting the sum of the "Amount" column connected to the different PO's from list 2 to be added in the "Used/Left" column in List 1 under the right PO. So List 1 is always showing the remaining amount on the different PO's

Even better if the sum of the amounts will be subtracted from the full amount in the "Amount" column in List 1

I am guessing using Calculated fields or workflows? I would prefer no workflows as i never made one ;)

Can anyone help me achieve this?

In my opinion, the flexible solution for your situation is creating Event Receiver on `Item Added` & `Item Updated` on list 1 to perofrm your calculation in a flexible manner!