Estimate vs Invoice: What's the Difference and When to Use Each

Estimates and invoices are two of the most commonly confused documents in small-business billing. They look almost identical on paper, but they have very different legal and operational meanings — and using the wrong one can either cost you a sale or cost you collected revenue.

What is an estimate?

An estimate (sometimes called a quote, proposal, or bid) is a non-binding document that tells a prospective client what your work will likely cost. It is sent before work begins and is used to win the engagement. An estimate is not a request for payment, and the client cannot pay it directly — they accept it (verbally, by email, or by signature) and you then proceed to do the work.

What is an invoice?

An invoice is a payment request. It is sent during or after work to formally request payment for goods or services provided. Invoices typically reference an agreed-upon price (often from an accepted estimate), include payment terms, and create a legal accounts-receivable record.

When to send each

• New client, undefined scope → send an estimate.
• Approved scope and ready to work → log it, then invoice on milestones.
• Repeat client with a known rate card → skip the estimate and invoice on completion.
• Project that may exceed the original estimate → send a revised estimate before doing the extra work, not after.

Convert estimates to invoices in one tap

QuickBill's Convert to Invoice action copies all line items, taxes, discounts, notes, and the client from any estimate into a new draft invoice. You can edit anything before sending — for example, splitting a $10,000 project estimate into two $5,000 invoices — and the original estimate stays in your records for reference.

QuickBill is available on the App Store. Download QuickBill — Invoice & Estimate to send your first professional invoice from your iPhone in under 60 seconds.