Good question, let me see if I can point you in the right direction.
The instructions for Item 12b are also listed on page 2 of the form and are as follows:
Enter the estimated cost to complete the contract. The contractor shall furnish estimates to complete that have been developed or updated within six months of the date of the progress payment request. The estimates to complete shall represent the contractor's best estimate of total costs to complete all remaining contract work required under the contract. The estimates shall include sufficient detail to permit Government verification.
Note: Bold italics added for emphasis.
Your contract should have FAR clause 52.232-16 Progress Payments (and 252.232-7004, DoD Progress Payment Rates, instead of Alternate I of the clause at FAR 52.232-16, if the contractor is a small business concern).
FAR 52.232-16 (g) provides guidance on what type of supporting data the contractor is required to submit in order for you to verify the amount is accurate. I’ll also point you to FAR 52.232-16(g)(ii):
“Include any additional supporting documentation requested by the Contracting Officer.”
For additional guidance on progress payments, you can read our Acquipedia article on the topic. If you require additional training on how to analyze contract costs, I’ll point you to our continuous learning module CLC 056 Analyzing Contract Costs.
Note: click to activate the links.