GST Invoice for Digital Marketing Services: The Agency Guide

I run an agency that invoices retainers every month, and I'll say the quiet part first: GST for a services agency is genuinely simple — one rate, one or two SAC codes, no inventory complications. Agencies get it wrong not because the law is hard but because nobody explains it in agency terms. This is the explanation I wish I'd had before our first registered invoice. (I'm a founder, not a CA — treat this as a working map and confirm your specifics with a professional.)

Do you even need to register?

Registration becomes mandatory when aggregate turnover crosses ₹20 lakh in a financial year (₹10 lakh in special-category states). Below that it's optional — but two things push agencies to register early. First, serious business clients prefer a GST invoice because the 18% comes back to them as input tax credit; an unregistered freelancer bill sits worse with their accountant than a proper tax invoice. Second, once registered you claim credit on your own inputs — software subscriptions, laptops, that co-working desk. We covered how GST interacts with your pricing in how much to charge for social media management: always quote "₹40,000 + GST", never an inclusive number.

Which SAC code goes on a digital marketing invoice?

Services use SAC (Services Accounting Codes) the way goods use HSN. For digital marketing there are two you'll actually use, both taxed at 18% (Busy's 2026 rate guide is a solid reference):

Since April 2021, B2B invoices must carry at least a 4-digit SAC (6-digit once your turnover crosses ₹5 crore). In practice: put the full 6-digit code on every invoice and never think about it again. The code doesn't change the 18% — it changes how cleanly your filings match your client's.

What must the invoice itself contain?

A compliant tax invoice for services needs, at minimum (ClearTax's invoice rules explainer has the full legal list):

• Your legal name, address and GSTIN; the client's name, address and GSTIN (for B2B)
• A consecutive serial number unique to the financial year — no ad-hoc "INV-final-2" numbering
• Invoice date, SAC code, description of services, taxable value
• Tax shown separately: CGST 9% + SGST 9% (client in your state) or IGST 18% (client in another state)
• Place of supply with the state name — this is what justifies the CGST/SGST-vs-IGST choice
• Whether tax is payable on reverse charge, and a signature or digital signature

Timing rule agencies routinely miss: a service invoice must be issued within 30 days of providing the service. For a monthly retainer, that means invoicing month-served + 30 days at the latest — not batching a quarter's invoices in one guilty evening, which also wrecks the client's credit-matching and your own cash flow.

A retainer invoice, concretely

Note what's not on it: the client's ₹50,000 Meta ad spend. The client should pay Meta directly. Routing ad spend through your invoice inflates your turnover (pulling registration and e-invoicing thresholds closer), makes you the float for someone else's ads, and muddies whether GST applies on money that was never your revenue.

Do you charge GST to clients outside India?

Genuine exports of services are zero-rated — if your client is outside India and pays you in convertible foreign exchange, you can invoice at 0% GST by filing a Letter of Undertaking (LUT) on the GST portal (a yearly, free filing). Without an LUT you'd pay IGST and claim a refund later, which is strictly worse for cash flow. For a remote-friendly agency this is the single highest-value GST fact: a US client retainer carries no GST at all, legally.

How do TDS and e-invoicing fit in?

• TDS: business clients deduct tax at source before paying (commonly 1–2% under Section 194C for advertising/contract work). Show GST as a separate line — TDS is then deducted on the taxable value, not on the GST component. Your ₹56,640 invoice arrives minus TDS on ₹48,000; reconcile against Form 26AS at filing.
• E-invoicing: mandatory only once turnover crosses ₹5 crore (threshold in force since 1 Aug 2023 — ClearTax). Most agencies are nowhere near it; just know the cliff exists so it doesn't surprise you in a good year.
• GSTR-1 discipline: your client's input credit shows up only after you report the invoice in your GSTR-1. File late and their accountant chases them, they chase you, and your next retainer conversation starts on the back foot.

One process note from running this monthly: the agencies that find GST painful are almost always the ones generating invoices in Word, numbering them by memory and tracking payments in chat. We built invoicing into the same workspace that runs delivery — GST-compliant invoices with SAC codes, recurring retainer billing and payment tracking next to the content calendar — precisely so month-end is a button, not a project. That's the finance layer of agency management software, and it matters more as you scale past the client count one spreadsheet can hold (the journey we mapped in how to start a social media marketing agency in India).

FAQ

Is GST registration mandatory below ₹20 lakh turnover?

No — registration becomes mandatory only once aggregate turnover crosses ₹20 lakh (₹10 lakh in special-category states). Many smaller agencies register voluntarily anyway, because business clients prefer GST invoices they can claim input credit on, and registration lets you claim credit on your own software and tool spends.

Which SAC code applies to social media marketing?

Use SAC 998361 for the marketing-services bundle — social media management, SEO, content and influencer marketing — and SAC 998365 when the line item is specifically running online ad campaigns. Both attract 18% GST, so a wrong pick doesn't change the tax, but a consistent code keeps client-side matching clean.

Can clients claim input tax credit on my invoice?

Yes — for a GST-registered business client, marketing is a business expense, so the 18% you charge flows back to them as input tax credit, provided your invoice carries both GSTINs and the SAC code, and you report it in your GSTR-1 on time so it lands in their GSTR-2B.