# GST Late Fee and 18% Interest: How They Are Calculated

> File your GST return late and you owe both a daily late fee and 18% annual interest on tax due. Here's how each is calculated.

- URL: https://www.pyalm.com/blog/gst-late-fee-calculator-guide
- Author: Fadhil Abdulla
- Category: Free Tools
- Published: 2026-06-21
- Updated: 2026-06-21

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## Two costs for a late GST return

Miss a GST filing deadline and there are two separate charges:

- **Late fee** — a fixed amount per day of delay (per Act, split across CGST and SGST), subject to a cap.
- **Interest** — 18% per annum on the net tax liability, charged for the period of delay.

The [GST Late Fee Calculator](https://www.pyalm.com/free-tools/gst-late-fee-calculator) works out both from your figures.

## How the interest works

Interest accrues only on the tax actually due, calculated day by day:

- Interest = tax due × 18% × (days late ÷ 365)

So a larger liability or a longer delay both push the cost up quickly.

## How the late fee works

The daily late fee depends on whether the return is a nil return or has tax due, and is capped at a maximum. Enter the days late and the tool applies the standard rate.

## How to use it

1. Enter your tax liability for the period.
2. Enter how many days the return is late.
3. The tool returns the late fee plus 18% interest.

## Avoid the charge entirely

The cheapest late fee is the one you never pay. Keeping returns ready on time is far simpler with organised books — see Pyalm's full set of [free finance tools](https://www.pyalm.com/free-tools).

[Open the GST Late Fee Calculator](https://www.pyalm.com/free-tools/gst-late-fee-calculator) | [India GST Calculator](https://www.pyalm.com/free-tools/gst-calculator)