Purchase Order vs Invoice: Key Differences Explained

Introduction

In business transactions, two documents appear in almost every deal: the purchase order and the invoice. They look similar, both involve numbers, and both connect buyers and sellers. But the truth is, they serve completely different purposes. A purchase order is created by the buyer to formally request goods or services at agreed terms. An invoice comes later from the seller, asking for payment once those goods or services have actually been delivered. If you’re running a business, even a small shop, knowing this difference is not optional. It’s like knowing the difference between ordering food and getting the bill afterwards

Understanding purchase order vs invoice keeps payments smooth, avoids messy disputes, strengthens internal control, and makes accounting far cleaner. If you’re running a business, even a small shop, knowing this difference is not optional. This guide breaks down what a purchase order really is, what an invoice is, how a sales invoice differs from a purchase invoice, and why the PO number is such a big deal in every organisation. 

What Is a Purchase Order?

Let’s start with the buyer’s side.

A purchase order, often called a PO, is a formal request sent by a buyer to a supplier before any goods or services are delivered. It’s not a payment, and it’s not a bill. It’s simply the buyer saying:
Here’s exactly what I want, in this quantity, at this price, delivered on this date.

Think of it like placing an online order on Amazon. You click “Buy Now,” choose quantity, view the price, select the address, and confirm. That order confirmation page? That’s basically your purchase order.

A simple example:

Imagine you run a small café. You need 10 kg of coffee beans every month. You message your supplier and say, “Send me 10 kg next Monday.”
If you keep doing this informally, sooner or later, someone will get the quantity, date, or price wrong.

A purchase order solves this.

You send a document that clearly mentions:

• Coffee beans – 10 kg
  
• Price per kg
  
• Total amount
  
• Delivery date
  
• Payment terms
  
• Shipping location
  
• Your signature/authorisation
  
• A unique PO number
  

This PO becomes the official record of what you ordered.

What a PO usually contains:

1. Item descriptions
2. Quantities
3. Unit prices
4. Delivery timeline
5. Billing and shipping details
6. Terms and conditions
7. A unique PO number

Each part exists so the supplier knows exactly what to send, and you know exactly what to expect. If anything goes wrong, the PO is your proof.

Why the PO number matters so much

That tiny PO number is the backbone of the whole transaction. It helps both sides:

1. Track the order
2. Match delivery vs request
3. Access past orders quickly
4. Resolve disputes
5. Pass audits
6. Record entries cleanly in accounting
   

In software like Vyapar, the PO number becomes the anchor that connects your order, delivery, and payments, so nothing gets lost.

What Is an Invoice?

Now flip to the seller’s side.

When people ask “what is an invoice,” they’re looking for the document a seller issues after supplying goods or services.

The simplest definition is:
An invoice is the seller’s official bill that asks the buyer to pay for what’s been delivered.

It’s the business version of the bill your waiter brings after you finish your meal.

A simple example:

Let’s go back to the café.
You placed a PO for 10 kg of coffee beans.
The supplier sends the beans on Monday, as promised.

Along with the delivery, they attach a document that says:

1. Coffee beans delivered: 10 kg
2. Price per kg
3. Taxes
4. Final total
5. Payment due date
6. Reference: Café’s PO number
7. Supplier’s invoice number

This is the invoice. You now owe them money based on it.

What an invoice usually contains:

1. Details of the goods delivered
2. Quantity and pricing
3. Taxes
4. Total amount due
5. Payment terms (7 days, 30 days, immediate, etc.)
6. Supplier’s invoice number
7. Reference to the buyer’s PO number
   

Every business depends on these details to track who owes what.

Types of Invoices: Sales vs Purchase Invoice

Even though the word “invoice” is the same, the perspective changes depending on who is looking at it.

1. Sales Invoice

• Issued by the seller
• Purpose: To claim payment
• For the seller, this is revenue.

2. Purchase Invoice

• Received by the buyer
• Purpose: To record expenses
• For the buyer, this is a cost.

A quick way to understand:

• If you’re sending the invoice → it’s a sales invoice
  
• If you’re receiving the invoice → it’s a purchase invoice
  

Same document. Two viewpoints. Two different roles in accounting.

Purchase Order vs Invoice: The Core Difference

Let’s boil it down to the simplest form:

• A purchase order is created by the buyer before the transaction.
• An invoice is created by the seller after completing the transaction.
• They flow in opposite directions.
• One authorizes a purchase.
•  The other demands payment.

Document Flow Table

Document	Created By	Sent To	Purpose
Purchase Order	Buyer	Seller	To request and authorise the purchase
Invoice	Seller	Buyer	To request payment and acts as proof of delivery.

Both documents remain connected through the PO number, ensuring everything matches from start to finish.

How Purchase Orders and Invoices Work Together

Here’s how the whole cycle plays out in real life:

1. Buyer creates a purchase order – A unique PO number is generated.
   
2. Seller ships goods or delivers services – They refer to the buyer’s PO.
   
3. Seller issues a sales invoice – This becomes the buyer’s purchase invoice.
   
4. Buyer verifies invoice vs PO – Did the seller send what was ordered?
    
5. This step is commonly known as the three-way match:
   
   • PO
   • Delivery note
   • Invoice
     
6. Payment is made – Only after everything matches.
   

It’s a simple system that prevents confusion and keeps accounting accurate. A tool like Vyapar makes this cycle easier because it keeps the PO, invoice, and stock all tied together.

Why Businesses Use Purchase Orders

Some people feel PO systems are only for large organisations. That’s not true at all. Even a home-based business benefits from POs because they:

• Reduce misunderstandings
  
• Create documented proof of every order
  
• Prevent unauthorised purchases
  
• Track expenses cleanly
  
• Make audits smoother
  
• Help manage budgets
  

A relatable example:

Say you run a small garment shop and regularly buy fabric from a wholesaler.
If you keep ordering verbally –
“Send me 50 meters of blue fabric…”
Sooner or later, someone will mishear it as “15 meters,” or you’ll forget what price you agreed on, or the supplier will assume the last rate still applies. A PO fixes all of this. 

Everything is written, dated, and acknowledged.
No surprises. No arguments.

Why Invoices Are Critical

Invoices aren’t just bills. They serve several essential functions:

• They create a legal obligation for payment
  
• They help sellers track receivables
  
• They help buyers record expenses
  
• They support GST, tax filing, and audits
  
• They help maintain clean accounts and cash flow
  

A relatable example:

Your café receives milk packets daily. The supplier gives you a monthly consolidated invoice. Without it, you wouldn’t even know exactly how much you owe or what quantity you actually received in that month.

The invoice becomes the backbone of your month-end accounting.

Purchase Order and Invoice Matching – Why It Matters?

When the PO and invoice don’t match, the trouble begins:

• Payments get delayed
  
• Suppliers follow up repeatedly
  
• Stock mismatches happen
  
• Account books show wrong entries
  
• Disputes rise
  

This is why companies rely on the three-way match before clearing any payment.

The PO number is the link that ties everything:

• What was ordered
  
• What was delivered
  
• What is being billed
  

When your system automatically matches these (like Vyapar does), life becomes much easier.

Key Differences At a Glance

Here’s a quick snapshot:

Concept	Purchase Order	Invoice
Created By	Buyer	Seller
Created When	Before goods/services arrive	After goods/services arrive
Purpose	To authorise a purchase	To request payment
Uses	Budgeting, approvals, and procurement control	Accounting, payment tracking
Contains	PO number, items, quantities, pricing	Invoice number, taxes, amount payable
Document Type	Contract of intent	Payment request

How Software Like Vyapar Helps

You don’t need fancy ERP software to manage POs and invoices. Even small and mid-sized businesses today prefer simple tools that:

• Create POs instantly
  
• Convert POs to invoices in one click
  
• Match stock automatically
  
• Keep supplier and customer records clean
  
• Help during audits
  
• Track payments
  
• Avoid duplicate purchases
  
• Maintain clean GST reporting
  

Vyapar fits naturally here because it’s built around the everyday workflow of Indian businesses. It connects POs, delivery challans, invoices, payments, and stock all in one place without complicating things.

You don’t feel like you’re using “software.” It simply becomes part of your daily routine.

Conclusion

Purchase orders and invoices may look similar, but they play very different roles. A purchase order is created before the transaction to authorise and document what the buyer wants. An invoice comes after the transaction to request payment for what was delivered.

Understanding the difference between them avoids confusion, improves communication, strengthens financial records, and keeps cash flow predictable. Whether you’re a small shop, a freelancer, a manufacturer, or a service provider, getting your PO-invoice cycle right is key to running a smooth business.

And if you use a system that links everything with a clean PO number, as tools like Vyapar do, the entire process stays transparent and hassle-free, from ordering to payment.