Work-Completion Certificate vs Invoice: Which Document You Need, When

“Send me the invoice,” says the client — and you panic, because you’ve already issued a “completion certificate” and you’re not sure if it’s the same thing. Same or different?

In short: a proforma invoice and an invoice (a request for payment) are usually the same thing. “Proforma” is just a more formal term. Some accounting systems distinguish them, but for a solo freelancer it’s the same piece of paper.

A work-completion certificate (act), however, is something else. Let’s break it down.

Quick comparison

	Invoice (request for payment)	Work-completion certificate
When to issue	Before payment	After the work is done
Purpose	A request: “Please pay this amount”	Confirmation: “The work was done and accepted”
Mandatory?	Usually — a business client won’t pay without an invoice	Yes — for the paper trail, especially with companies
What it contains	List of services/goods, prices, payment details, due date	List of what was done, fact of acceptance, both parties’ signatures
Client’s signature	Not required	Required
What the client does with it	Passes it to accounting → they pay	Files it → writes off the expense

In plain words

1. First — the invoice. You say: “Here are the services, here’s the amount, here’s where to pay.”
2. The client pays.
3. You do the work (if not already done; or you confirm what’s been delivered).
4. You issue the completion certificate. You say: “I confirm the work was done and the client accepted it.”

In some setups the invoice is issued after the work (post-paid). In others, before (prepaid). The logic doesn’t change.

Why companies ask for both

Because they are two different documents with different purposes:

• The invoice is the basis for transferring funds from the client’s bank. Without it, accounting won’t release the payment.
• The completion certificate is the basis for writing off the expense in the client’s books. Without it, the expense is left “hanging.”

For you, that means: on a single project with a business client you usually issue both documents. First the invoice, then — after delivery — the certificate.

”But an individual is paying me — do I need both?”

If the client is a private individual, an invoice alone is usually enough. The certificate is optional, for your own order.

In practice, many freelancers just issue a single certificate after everything is done — both as proof of work and as the payment details. It’s not strictly by the book, but it’s common and usually causes no problems.

Common mistakes

1. Calling a certificate an invoice. The client opens your PDF and it reads “WORK-COMPLETION CERTIFICATE” — but they wanted an invoice, because they haven’t paid yet. That confuses them and delays payment. Issue the right document.

2. One document instead of two. Some people merge them into an “invoice-certificate.” That’s non-standard, and some clients’ accounting teams will be confused. Two separate documents are better.

3. Certificate date = invoice date. No. The certificate date is the date the work was accepted — usually after the client has paid and received the result. Otherwise it’s a weak point legally.

How it works in Minteo

In one workflow, both PDFs are generated from the same data:

• Click “Create invoice” → get the “Invoice” PDF.
• Work done, payment received → same record → “Download certificate” → get the “Work-completion certificate” PDF.

Details, descriptions, amounts, signatures — identical and reconciled automatically. No need to build a separate Word table and copy data across.

Conclusion

• The invoice is about money. Before payment.
• The completion certificate is about the work. After delivery.

With a business client you usually issue both. With an individual, one is usually enough (typically a certificate that doubles as payment details).

If you want both documents in one click, straight from real hours in your tracker — try Minteo.