Input tax versus output tax: how the adjustment works
Sales tax is a tax on value added, and the mechanism that makes it so is the input tax adjustment. Get the adjustment right and the tax is broadly neutral to your business. Get it wrong and it becomes a real cost — which is what happens to most businesses that treat input tax as automatic.
The monthly computation
| Term | What it is |
|---|---|
| Output tax | Tax you charged on your taxable supplies during the period |
| Input tax | Tax charged to you by registered suppliers, and tax paid on imports |
| Claimable input tax | The subset of input tax the law allows you to adjust |
| Carry forward | Excess claimable input over output, applied against future periods |
The four tests every input has to pass
The mechanism is section 7 of the Sales Tax Act 1990 — a registered person deducts input tax from output tax for the period — and the limits are in section 8, which lists what may not be deducted at all. Almost every disallowed claim is a section 8 question, not a section 7 one: the arithmetic was right and the input was never admissible.
- Is it permitted? Certain categories of input tax are blocked by law irrespective of business purpose. A blocked input is a cost, not a claim.
- Does it relate to your taxable activity? Input tax on purchases used to make exempt supplies is generally not claimable, and purely personal purchases never are.
- Is the documentation valid? A tax invoice from a registered supplier carrying all mandatory particulars, or the prescribed import documentation. See invoice requirements.
- Is it within time? Input tax must be claimed within the prescribed period. Late is lost.
An input that fails any one of the four is not claimable, however commercially obvious the expenditure was.
We settle the taxable value, apportion input tax and file monthly with the right federal or provincial authority.
Avail our sales tax servicesWhere claims are most often disallowed
- Invoices with defective particulars — a missing or incorrect registration number is the single most common defect.
- Suppliers who were not active at the time of supply, or whose registration cannot be verified.
- Purchases relating to exempt supplies, claimed in full rather than apportioned.
- Reduced-rate and zero-rated services under provincial regimes, where input recovery is restricted as the trade-off for the lower output rate — Punjab services tax.
- Personal or non-business expenditure routed through the business account.
- Claims made outside the time window because the invoice arrived late and was posted later still.
Apportionment for mixed supplies
Businesses making both taxable and exempt supplies cannot claim everything. Where a purchase serves both — rent, utilities, shared overheads — an apportionment is required.
Two disciplines matter more than the method chosen. First, identify wholly-attributable inputs separately before apportioning the residue — treating everything as shared understates your claim. Second, apply the same method every month. A method that changes when it happens to help is the one that gets challenged.
When input exceeds output
A credit position arises for exporters, businesses in a capital investment phase, and seasonal businesses. Generally the excess carries forward against future output tax rather than being refunded on demand. Refunds are available in defined circumstances — notably for zero-rated exporters — through a claim process with its own evidence requirements.
Practical consequences: track the carry-forward balance formally rather than letting it live inside the portal, and reconcile it month to month. An unreconciled credit that has drifted is difficult to substantiate later. See filing the return.
The monthly controls that protect the claim
- Check every supplier invoice on receipt. Particulars, registration number, rate, description, arithmetic.
- Verify supplier status before payment, not at audit — sales tax active list.
- Post purchases in the month they belong to, so nothing falls outside the claim window.
- Maintain the purchase register at invoice level, not as a monthly total.
- Reconcile the register to the return annexure, and the return to the ledger, every month.
- Record the apportionment working with the return, so it can be reproduced two years later.
These are the same records an audit tests, so maintaining them monthly is not extra work — it is the work done at the right time. See sales tax audit preparation.
Sources
This guide is written against the official and clearly labelled professional references below. Rates, thresholds and portal procedures change between reviews, so open the primary source before relying on a figure.
- Sales Tax Basics (FBR)
- Sales Tax Act 1990, amended through 30 June 2026 (FBR)
- File a Sales Tax Return (FBR)
Questions people also ask
Can I claim input tax on everything my business buys?
No. Claimability depends on the law permitting it, the purchase relating to your taxable activity, and the documentation supporting it. Certain categories are blocked outright, purchases relating to exempt supplies are generally not claimable, and anything without a valid tax invoice from a registered supplier is not claimable regardless of how genuine the expense was.
What happens if my input tax exceeds my output tax?
The excess generally carries forward against future output tax rather than being refunded automatically. Refunds are available in defined circumstances, notably for zero-rated exporters, through a claim process with its own evidence requirements. For most businesses a credit position simply reduces next month liability.
My supplier charged me tax but is not on the active list. Now what?
Your claim is at risk. Claiming input tax against a supplier who was not active, or whose registration particulars do not check out, is one of the most common disallowances. Verify supplier status before you pay rather than at audit, and treat an unverifiable supplier as a commercial risk as well as a tax one.
We make both taxable and exempt supplies. How much input can we claim?
Input tax attributable to taxable supplies is claimable; input tax attributable to exempt supplies generally is not. Where a purchase serves both, an apportionment is required on a reasonable and consistently applied basis. Document the method you adopt and apply it every month rather than recalculating it in a way that happens to favour each period.
Is there a time limit for claiming input tax?
Yes. Input tax must generally be claimed within a prescribed period, and a claim made outside that window is lost even where the invoice is perfectly valid. That is why supplier invoices need collecting and posting monthly rather than accumulating in a drawer — a late-arriving invoice can become an unclaimable one.
Send the tax year and the transaction or filing involved, and we will tell you what is actually required.
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