What is the similarity of the initial invoice and estimate?

An estimated and initial invoice is not a request for payment, and it typically includes the type, amount and cost of items, as well as other pertinent data like shipping charges and taxes.

A quote is a formal estimate that shows the products or services needed, and the monetary amount for those products or services. A quote can be verbal or written, it may or may not be the exact same as the end product, in terms of products, services, and the dollar amount owed. A quote lets you know how much you will owe for the projected work or service, and it insures you will only owe that amount, and not some a number that is completely random.

On the other hand, an invoice is a detailed list of products that have already been sold or services that have already been completed. Aside from the list, the invoice also includes dates as to when the products were sold or the services were completed, along with the monetary amount owed for each line item or the total amount that is owed from the customer.

With respect to similarities, both contain list of products to be supplied or services to be rendered and the monetary values for those products or services.