Quotation vs. proforma invoice
A proforma invoice is a non-official invoice that’s sent to a customer before the final details of a sale are confirmed. They’re often used at the same point in the sales process as a quotation; however, quotes and proforma invoices serve slightly different purposes.
A quotation would normally be sent if a customer makes an enquiry, or if they want to find out more about a product or service. A proforma invoice is sent if a customer has committed to a purchase, but can’t be sent a true invoice because the final details of the sale are not certain.
Quotation vs. estimate
Like quotations, estimates are sent to customers who enquire about a product or service. However, a quotation requires clear paraments (time, labour, raw materials, etc.) and relatively stable costs, which means that some businesses cannot give quotations because it simply isn’t possible to give a fixed price.
Instead of issuing a quotation, these businesses would issue an estimate, which is a non-binding approximation of what a job is likely to cost.