How Is GST Interest Calculated? A Simple Guide with Examples

A delayed GST payment can add to your business costs. Understanding how interest works helps you calculate the amount accurately and plan your payments better.

The calculation needs three inputs: the amount on which interest applies, the annual interest rate, and the number of days involved.

What is GST interest?

GST interest arises when tax remains unpaid beyond its due date. Interest can also apply when input tax credit (ITC) has been wrongly availed and utilised. For delayed tax payments, interest generally starts from the day after the payment due date. For wrongly availed and utilised ITC, the relevant period runs from utilisation until reversal or payment, as prescribed under Rule 88B. GST interest handbook

Which interest rate applies?

The general annual rate is 18% for delayed GST payments and 18% for wrongly availed and utilised ITC. The infographic’s 24% figure for ITC needs updating: the notified rate was reduced to 18%, retrospectively from 1 July 2017. Merely availing incorrect credit without utilising it does not, by itself, trigger interest under Section 50(3). GST interest handbook

The GST interest formula

For a straightforward calculation using an annual rate entered as a whole number:

Interest = Amount × Annual rate × Number of days ÷ 36,500

For example, enter 18 for an annual rate of 18%. This calculates simple interest.

Before applying the formula, identify the correct amount. For qualifying delayed returns, interest generally applies to the tax paid through the electronic cash ledger, subject to statutory exceptions. GST interest handbook

A further rule excludes qualifying money deposited in the cash ledger by the return due date, retained there, and subsequently used to pay tax when filing that return. Government explanation of the Rule 88B amendment

Example 1: ₹12,000 paid 25 days late

Assume ₹12,000 is the amount attracting interest at 18% annually.

Interest = ₹12,000 × 18 × 25 ÷ 36,500
Interest = ₹147.95, or approximately ₹148.

Example 2: ₹75,000 paid 40 days late

Using the same annual rate:

Interest = ₹75,000 × 18 × 40 ÷ 36,500
Interest = ₹1,479.45, or approximately ₹1,479.

These examples assume the entire stated amount attracts interest throughout the stated period.

Quick reference table

Amount attracting interest	Days	Annual rate	Calculated interest
₹10,000	25	18%	₹123.29
₹25,000	15	18%	₹184.93
₹75,000	40	18%	₹1,479.45
₹1,50,000	30	18%	₹2,219.18

Calculate GST interest in Excel

Set up your worksheet with:

• A2: Amount attracting interest

• B2: Number of days

• C2: Annual interest rate entered as 18

Then enter:

=ROUND(A2*B2*C2/36500,2)

If C2 is formatted as a percentage and contains 18%, use:

=ROUND(A2*B2*C2/365,2)

The daily cost is easy to see: at 18% annually, ₹10,000 attracts approximately ₹4.93 in interest per day. Keeping payment dates, return records, and ledger balances organised makes it easier to calculate interest correctly and address delays promptly.

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