Here is my scenario:Service technicians go to a job site and performs work.  As per the instructions on his service ticket he is to collect $100 from the customer.  However he had to use an additional part costing $50.  Also, there was a part from the original order he did not use that cost $25 and he needs to remove that from the amount owing.So I have created a form for Change Orders.  The first tab I created is Original Balance and is set to Collect Payment.  The next tab is where the tech enters the cost of the parts added and is set to Collect Payment.  The next tab is where the tech enters the negative cost of the parts not used and is set to Collect Payment.  However the payment is not affected when a negative value is put in.So it should be $100+$50+(-$25)=$125However I get:$100+$50+(-$25)=$150Am I doing something wrong?
Cognito Forms - Subtracting Calulations
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Cognito Forms does support negative amounts when collecting payment.  However, we prevent negatives from appearing on an invoice based on user input to protect our customers from scenarios like this:Cognito Forms customer creates a registration form for an charity event, charging $85 per ticketForm also includes an additional donation amount field on the formIn this case we prevent negatives by default for the donation field to prevent someone from entering a negative amount and thus getting a discount on their tickets.However, you can definitely include negatives as long as you use the Price field. In your case, just add a Price field near the field where they are entering the amounts.  Set the calculation for the Price field to pull the value from the original field.  You can even allow them to enter a positive amount for the part and make it negative in your calculation.  Then mark the Price field as hidden so it will only appear on the invoice, not the form.  Clear the Collect Payment setting for your original field.Using this approach, you can force Cognito Forms to accept the negative deduction from the invoice.  You can even use a Repeating Section to capture each part and the amount and have both the part description and amount reflected on the invoice using the Price field, since you can also calculate the line item name and description.