Welcome and good day to you also, @Melyssa1.

I know how to add a column for Markup in your Invoice and Estimate form, and I'll gladly assist you with this.

Please know that after you add the Markup column, it won't calculate the amount automatically. You'll need to calculate the amount manually and place it there.

Let's start by adding the column to your Invoice form. You can add it in the Formatting section when you create an invoice transaction. Here's how:

1. Go to the Customers tab and select Create Invoices.
   
   
2. Click the Formatting option above the invoice form.
3. Beneath that option, pick Customize Data Layout.
   
4. Go to the Columns section.
5. Tick the boxes of the Screen and Print column beside the "Other 1" option and select what Order you want for the Markup column. Then, change the name to Markup in the Title section.
6. Once done, click OK.

Also, check the Template used when adding the column since this only applies to that invoice template. If you want to see the Markup column on all invoice templates, repeat the steps above for each of them.

To add the Markup column to the Estimate form, go to the Customer tab and select Create Estimates. Then, follow the steps above, and the Markup column will appear in the form.

You may want to learn how to modify sales form templates before sending them to your customers. Check out this article: Use and customize form templates.

Please return here if you have additional questions about managing your invoice and estimates form. We'll assist you as soon as possible. Take care, and have a good one.

@Melyssa1  RE: We want to be able to have a column on our estimates and invoices where we can change the markup as we go. 

Unfortunately there's no way to create a column that impacts the invoice calculation. The custom field @Bryan_M  recommended will function like a memo/text and won't have any actual impact on the Amount.

Some versions of QuickBooks include a feature called Price Levels which may help. Check in your preferences to see if you have this feature. Start at Edit | Preferences | Sales & Customers | Company Preferences and see if you have a section there for Custom Pricing: