The short answer
An estimate tells a client what a job will cost before you start. An invoice tells a client what they owe after the work is done. They serve different purposes, but the best ones look professional and contain clear numbers.
What an estimate is
An estimate is a document you give a client before the job begins. It outlines the scope of work, the materials involved, your labor rate, and the expected total. It's your proposal — and getting it signed is how you protect yourself from scope creep and disputes.
Estimates are usually not legally binding, but a signed estimate is a strong record of what was agreed. Some contractors use the word "quote" for a fixed price and "estimate" for a price that may vary based on conditions discovered during the job.
What an invoice is
An invoice is a payment request. You send it after the work is complete (or after a milestone, for phased projects). It should reflect exactly what was done — if anything changed from the original estimate, note it on the invoice with a brief explanation.
A professional invoice includes your business details, the client's details, a unique invoice number, an itemized breakdown of work and materials, the total due, and your payment terms.
Converting an estimate to an invoice
The cleanest workflow is estimate → approval → invoice. Get the estimate signed, do the work, then convert it directly to an invoice. Good invoicing apps like BIG INVOICE do this in one tap — no retyping, no starting from scratch.