Sales Order vs Purchase Order: What Each One Does

In B2B trade, almost every sale starts with an order. The buyer sends a purchase order; the seller responds with a sales order; goods move; an invoice follows. Small businesses often skip one or both documents, then struggle when a buyer's accounts team asks, "Which PO is this against?"

This guide explains the difference between a sales order and a purchase order, how both connect to the GST invoice, and how to use them to get paid faster.

What is a purchase order?

A purchase order (PO) is a document issued by the buyer to a supplier. It states what the buyer wants to purchase and on what terms. A typical PO contains:

• PO number and date
• Buyer's name, address and GSTIN
• Supplier's name and address
• Item description, specifications, quantity and unit price
• Taxes, or a note on how GST will apply
• Delivery date and address
• Payment terms
• Terms and conditions (warranties, penalties, inspection)
• Authorised signature

For the buyer, the PO is an internal control: it records that someone with authority approved the spend. For the supplier, it is confirmation that the buyer is committed.

What is a sales order?

A sales order (SO) is a document issued by the seller after receiving an order. It confirms what the seller will supply, at what price and when. A typical SO contains:

• SO number and date
• Reference to the customer's PO number
• Customer details and delivery address
• Items, quantities, prices and expected tax
• Delivery schedule
• Payment terms

For the seller, the SO drives internal work: it tells the warehouse what to pick, production what to make and accounts what to invoice. Some businesses send the SO to the customer as an order acknowledgement; others keep it internal.

Sales order vs purchase order: side-by-side

Point	Purchase order	Sales order
Issued by	Buyer	Seller
Sent to	Supplier	Customer (as acknowledgement) or internal
Purpose	Authorise and request a purchase	Confirm and plan a supply
Records	Buyer's commitment to buy	Seller's commitment to supply
Triggers	Supplier's sales order and delivery	Picking, production, dispatch, invoicing
Recorded in	Buyer's purchase system	Seller's sales system
GST tax document	No	No
Reported in GST returns	No	No
Links to	Goods receipt note and supplier invoice	Delivery challan or dispatch and tax invoice

Remember: one deal, two perspectives. The buyer's PO and the seller's SO describe the same transaction.

How do PO, SO and invoice fit together?

1. Quotation — the seller quotes a price. See quotation vs estimate vs invoice.
2. Purchase order — the buyer issues a PO based on the quote.
3. Sales order — the seller records the PO as an SO and confirms.
4. Dispatch — goods move with the tax invoice, or with a delivery challan where the movement is not a sale (see delivery challan under GST), and an e-way bill if required.
5. Goods receipt note (GRN) — the buyer records what actually arrived and was accepted.
6. Tax invoice — the seller's invoice, quoting the PO number. For goods, issued at or before removal or delivery.
7. Three-way match — the buyer matches PO, GRN and invoice before paying.
8. Payment and receipt — the buyer pays; the seller issues a receipt.

Only step 6 is a GST tax invoice. The PO and SO are commercial documents; they carry no tax liability and are not reported in GSTR-1.

Worked example: a three-way match

A Ludhiana bicycle-parts manufacturer receives a PO from a registered assembler in Punjab (same state, so CGST+SGST).

Purchase order PO-7781:

Item	Qty	Rate (₹)	Value (₹)
Steel rims 26"	500	340	1,70,000.00
Spoke sets	500	110	55,000.00
Total before tax			2,25,000.00

Payment: Net 30 from GRN date.

Sales order SO/26-27/0219 mirrors the PO.

Dispatch: the factory has only 460 rim sets ready and ships 460 rims and 500 spoke sets.

GRN at the assembler: 460 rims accepted; 500 spoke sets received, but 12 rejected on inspection, so 488 accepted.

Tax invoice INV/26-27/0904 (based on what was supplied, GST assumed at 18%):

Item	Qty	Rate (₹)	Value (₹)
Steel rims 26"	460	340	1,56,400.00
Spoke sets	500	110	55,000.00
Taxable value			2,11,400.00
CGST @ 9%			19,026.00
SGST @ 9%			19,026.00
Total			2,49,452.00

Matching: the assembler's system flags 12 spoke sets invoiced but rejected. The manufacturer issues a credit note for 12 × ₹110 = ₹1,320 plus GST of ₹237.60 (₹118.80 CGST + ₹118.80 SGST), total ₹1,557.60. The net amount payable becomes ₹2,49,452.00 − ₹1,557.60 = ₹2,47,894.40. See credit note under GST.

The remaining 40 rims stay open on the PO until shipped or cancelled.

Why do buyers insist on a PO number on your invoice?

Large buyers route invoices through accounts payable systems that match each invoice to an approved PO. An invoice without a PO number often sits in an exceptions queue. Quoting the PO number, the PO line items and the GRN reference where known is one of the simplest ways to get paid faster.

Types of purchase orders

Type	What it covers	Example
Standard PO	One-time purchase of defined items	200 office chairs
Blanket PO	Repeated purchases over a period at fixed rates	Packaging material for a year
Contract PO	Terms agreed, quantities and items set later	Master agreement with a logistics vendor
Planned PO	Quantities known, delivery dates scheduled later	Monthly release of components

Each delivery against a blanket or planned PO is invoiced separately, quoting the PO and release number.

What should you check before accepting a purchase order?

Before you confirm a PO with a sales order, compare it line by line with your quotation:

1. Items and specifications match what you quoted.
2. Quantities are what you can supply, and by the date requested.
3. Rates match the quotation, and GST is either shown correctly or noted as extra.
4. Delivery address and state are clear, because they affect place of supply and whether you charge IGST or CGST+SGST.
5. Buyer GSTIN is correct; check it with the GSTIN validator.
6. Payment terms match what you agreed. A PO that says Net 60 when you quoted Net 30 needs to be raised before you supply.
7. Penalty clauses for late delivery or quality are acceptable.
8. Billing instructions such as invoice address, portal upload or documents to attach are noted.

If anything differs, ask for an amended PO before dispatch. Fixing a mismatch after the invoice is raised usually means a credit note, a fresh invoice and weeks of delay.

Do small businesses really need sales orders?

If you take only a few orders a week, the PO plus your invoice may be enough. Sales orders earn their place when you have partial deliveries, back orders, several people involved in dispatch or stock that must be reserved for confirmed customers. They also give you an "orders in hand" view, which helps plan purchases and cash flow.

How do you handle changes to a PO after it is issued?

Orders change: quantities rise, delivery dates move, prices are renegotiated. Handling this cleanly avoids invoices that no longer match anything.

1. Buyer issues a PO amendment, quoting the original PO number with a revision suffix (for example PO/26-27/0311 Rev 1) and stating only what changed.
2. Seller updates the sales order to match, keeping the old version for reference.
3. Seller confirms the amendment in writing, especially if price or delivery dates moved.
4. Invoices quote the PO and revision they relate to, so the buyer's accounts team can match them.

Partial deliveries and backorders

When a sales order is delivered in parts, each dispatch gets its own tax invoice for what actually moved. The sales order stays open for the balance. A simple tracking table helps:

SO line	Ordered	Invoiced so far	Balance
Steel rims 26"	500	460	40
Spoke sets	500	500	0

When the remaining 40 rims ship, a second invoice is raised for 40 × ₹340 = ₹13,600 plus GST, and the sales order closes.

Cancelling an order

If the buyer cancels before dispatch, close the sales order as cancelled; no tax invoice is needed for goods never supplied. If an advance was received, deal with it as covered in advance payment under GST.

Common mistakes

• Supplying without a PO from a buyer who requires one, then waiting months for payment.
• Invoicing the PO quantity instead of the quantity actually supplied.
• Not reading PO terms such as penalties for late delivery or longer payment periods than your quotation.
• Prices on the invoice that differ from the PO without a written amendment.
• Treating the PO as the invoice. A PO is not a tax document; the buyer cannot claim credit on it.
• Losing track of open PO balances, so partial deliveries are never completed or closed.
• Missing the PO number on the invoice, the most common and most avoidable cause of delay.

How software links orders and invoices

When orders and invoices live in the same system, the SO converts into a tax invoice with the PO number, items and prices carried over, and you only adjust actual quantities. Billing Software by Betterwork, for instance, raises GST invoices with HSN codes, generates e-way bills where required, tracks stock with batch and expiry details and issues credit notes for rejections, which keeps the three-way match tidy for your buyers. To see this workflow, book a demo.

What about purchase orders you issue to your own suppliers?

The same logic works in reverse when you buy. Issuing your own purchase orders to suppliers gives you:

• Price control. The supplier's invoice is checked against the rate you agreed, not the rate they remember.
• Cleaner input tax credit. Matching supplier invoices to POs and goods received makes it easier to reconcile purchases with GSTR-2B. See GSTR-2B reconciliation.
• Budget discipline. Only approved purchases get paid.

Even a simple numbered PO from your billing software, sent on WhatsApp or email, is better than a phone order with no record.

Key takeaways

• The buyer issues the purchase order; the seller issues the sales order.
• Both describe the same deal from opposite sides, and neither is a GST tax invoice.
• The tax invoice is raised on actual supply and should quote the PO number.
• Buyers pay after matching PO, GRN and invoice; mismatches cause delays.
• Handle rejections and shortfalls with credit notes and open PO balances.

This guide is general information, not tax advice. Rules last checked on 20 October 2026; confirm with your tax professional for your situation.