GST on interest on delayed payment follows from section 15(2)(d) of the CGST Act, 2017, which says the value of a supply shall include interest or late fee or penalty for delayed payment of any consideration. The interest is not treated as a separate financial item sitting outside GST. It attaches to the supply it relates to. The same sub-section also pulls in cesses and fees charged separately, incidental expenses, and certain subsidies, which is why the taxable value of a contractor’s bill is often larger than the rate multiplied by the quantity.

Chasing a delayed payment is the least enjoyable part of contracting. When the money finally moves and you are entitled to interest on top, it feels like recovery rather than revenue.

The Act does not see it that way. Section 15 decides what your bill is worth for tax, and interest for late payment is on the list of things it adds in.

Start with what section 15(1) says the value is

Section 15(1) of the CGST Act sets the default. The value of a supply is the transaction value, which is “the price actually paid or payable for the said supply”, provided two conditions hold: the supplier and the recipient are not related, and the price is the sole consideration for the supply.

That is the ordinary case for a contractor billing an unrelated client at an agreed rate. If either condition fails, section 15(4) says the value is worked out in the prescribed manner instead.

So far, straightforward. The work is in sub-section (2), which lists what gets added to that price.

GST on interest on delayed payment comes from clause (d)

Section 15(2)(d) is short enough to quote whole. The value of supply shall include:

“interest or late fee or penalty for delayed payment of any consideration for any supply”.

Three things are worth drawing out of that line.

It names three different labels: interest, late fee and penalty. Calling the charge something other than interest in your contract does not move it outside the clause.

It attaches to delayed payment of consideration for a supply. This is not about interest in general. Interest on a fixed deposit or on a loan you have given is a different question entirely. This clause is about money owed to you for work you did, paid late.

And it says the value shall include it. The interest rides on the supply it relates to rather than standing alone.

In practice this bites at exactly the moment a contractor feels least like paying more tax. You have carried a receivable for eight months, you have finally negotiated or claimed interest on it, and that recovery arrives already carrying a tax consequence. Contractor payment delays on government work covers how the interest claim itself is built; this is what happens to it afterwards.

One honest caveat. Interest that arises under a statute rather than under your contract has been argued about, and the answer can turn on the facts and on how the claim is framed. The provision above is what the Act says on its face. Put your own situation in front of a tax adviser before you decide how to bill it.

When the tax on that interest actually falls due

Section 15 decides that the interest is inside the value. It does not say when you have to pay tax on it, and that is a separate question with its own answer.

Section 13(6) deals with it in one sentence. The time of supply, to the extent it relates to an addition in the value of supply by way of interest, late fee or penalty for delayed payment of any consideration, shall be the date on which the supplier receives such addition in value.

Read that against the rule for the work itself and the contrast is the useful part. For the underlying supply, section 13(2) fixes the time of supply at the earlier of your invoice or your receipt of payment, which is how a contractor ends up owing tax on a bill the client has not paid. For interest on a late payment, section 13(6) uses one date only: the date you actually receive it.

So a claim for interest sitting in a letter, a running account, or an arbitration file does not carry a GST liability while it sits there. Debiting the client’s account in your own books does not start the clock either, because the sub-section turns on receipt of the addition in value rather than on the raising of a demand. The liability attaches when the money arrives, and it falls into the return for that period.

That is worth knowing before you bill. An interest claim raised with the final bill and recovered two years later is taxable in the period of recovery, not the period of the claim, so the tax comes out of money you are holding rather than money you are still chasing. It is the opposite of the mobilisation advance position, where the tax falls due on receipt before any bill exists. Both are receipt-driven; only one of them hurts. Where these amounts end up being reconciled across the year is the annual return — see GSTR-9 annual return for contractors.

What else section 15(2) adds

Clause (d) is one of five. The others catch contractors just as often.

Clause What gets added to the value Typical site example
15(2)(a) Taxes, duties, cesses, fees and charges under any law other than the GST Acts, if charged separately A cess or fee you show on its own line
15(2)(b) Any amount you were liable to pay for the supply, but which the client incurred, and which is not already in the price Client settles a charge that was your obligation
15(2)(c) Incidental expenses, including commission and packing, and anything charged for work done at or before supply Mobilising, shifting, handling charged on top
15(2)(d) Interest, late fee or penalty for delayed payment of consideration Interest recovered on an overdue RA bill
15(2)(e) Subsidies directly linked to the price, excluding Central and State Government subsidies A price-linked subsidy from a non-government source

Clause (a) is the one that surprises people most. Contractors often assume that showing a statutory charge on a separate line of the bill keeps it out of the taxable value. The clause says the opposite: amounts levied under any other law, if charged separately by the supplier, are included. Separating a line item is a presentation choice, not a tax outcome.

Clause (b) catches the informal arrangement where the client pays something directly that was contractually yours to pay, and everybody treats it as outside the bill. If it was your liability in relation to the supply and it is not in the price, section 15(2)(b) adds it back.

Clause (c) reaches “any amount charged for anything done by the supplier in respect of the supply at the time of, or before delivery”. Mobilisation and handling charges added on top of the rate sit squarely there. On the timing of an advance against that same work, see GST on mobilisation advance.

Discounts are the one thing taken out, on conditions

Section 15(3) works the other way, and it is strict about how.

A discount given before or at the time of supply is excluded if it has been duly recorded in the invoice issued for that supply. Straightforward: record it on the bill.

A discount given after the supply is excluded only if both of these hold:

  • it was established in terms of an agreement entered into at or before the time of the supply, and is specifically linked to relevant invoices; and
  • the input tax credit attributable to the discount has been reversed by the recipient, on the basis of a document issued by you.

That second condition is the one that fails in real life. A rebate negotiated months later, with no prior agreement and no reversal at the client’s end, does not reduce the value of supply however genuine the commercial concession was. If you expect to settle at less than billed, the time to write it into the agreement is before the work, not during the argument.

Why this matters more than it looks

Section 15 is not a compliance detail. It decides the base that every other GST number is calculated on.

The deduction a government client makes from your bill runs on the taxable value, which is why GST TDS on works contract is worked out after stripping the tax but on everything section 15 has added in. If you are weighing the simpler route instead, the GST composition scheme for contractors changes the picture again, because there you can neither collect tax nor claim credit.

The practical habit is small. When you price a job, price the additions too, not just the rate. Mobilisation, handling, any charge you intend to raise separately, and the interest you expect to claim if payment runs late. If those are priced as though they are outside the tax and section 15 says they are inside it, the shortfall comes out of your margin.

Add delayed payment interest to your taxable value

Interest for late payment is part of the value of the supply under section 15(2)(d), not a separate recovery that sits outside GST. The same sub-section adds separately-charged cesses and fees, costs the client bore that were yours, incidental and pre-delivery charges, and price-linked subsidies other than government ones.

Discounts come out only on the conditions in section 15(3), and the after-the-fact ones usually fail them. Build both sides into the quote rather than discovering them at filing. On the interest itself, section 13(6) gives you the one piece of good news in this area: it is taxable when you receive it, not when you claim it.

Working out whether the next machine pays for itself on contracts like these? The equipment finance section sets out what lenders look at, and retention money in a construction contract covers the other amount that never quite arrives on time.

Tax provisions and their interpretation change, and the treatment of statutory interest can turn on your own facts. Confirm current terms with a qualified tax adviser or the official source before relying on anything described here.