GST interest calculator
Enter the tax amount discharged in cash and the relevant dates. Use the cash-ledger field only where the balance qualifies under the applicable rule.
For an ordinary delayed GSTR-3B payment, interest is generally estimated on the tax liability discharged through the electronic cash ledger, not automatically on the gross tax before available input tax credit. The basic formula is chargeable tax × annual interest rate × days of delay ÷ 365. Late fee is a separate return-filing charge. Portal computation, cash-ledger history, retrospective declarations and special notifications can change the final amount.
GST interest is time-based. A one-day difference in the discharge date, an incorrect due date or use of the wrong cash-liability figure can change the result.
Before calculating, identify the tax period, return type, original due date, date of cash-ledger debit, portion discharged through cash and any continuously available eligible cash balance.
What is GST interest?
Section 50 of the Central Goods and Services Tax Act governs interest on delayed payment of tax. Interest is a statutory charge for the period during which tax remains unpaid; it is not the same as a discretionary penalty.
The government notifies the annual rate within the maximum permitted by the Act. The rate commonly applied to delayed payment under section 50(1) is 18% per annum, while specified cases involving undue or excess input tax credit or output-tax reduction can attract a different notified rate.
Interest, late fee and penalty arise under different provisions and should be calculated and reported separately.
When does GST interest apply?
| Situation | Possible consequence | Calculation focus |
|---|---|---|
| GSTR-3B filed after the due date with tax payable in cash | Interest under section 50(1), subject to the statutory proviso | Cash portion of tax and delay period. |
| Earlier-period liability reported in a later return | Interest may apply from the original due date for the liability | Original tax period and actual discharge date. |
| Reverse-charge liability paid late | Interest may apply because the liability generally requires cash payment | Relevant cash liability and delay. |
| Input tax credit wrongly availed and utilised | Section 50(3) may apply at the notified rate | Amount wrongly availed and utilised and the prescribed period. |
| Return filed late but no tax payable | Interest may be nil, but late fee can still apply | Separate section 47 late-fee rules. |
GST interest formula
Interest = chargeable tax amount × annual rate × number of delayed days ÷ 365.
Example: ₹10,000 of chargeable tax is discharged 10 days late at 18% per annum.
₹10,000 × 18% × 10 ÷ 365 = ₹49.32.
The day count should be checked from the day after the applicable due date until the date of discharge. Extensions, notified relief and portal-specific calculation rules can alter the period.
How the electronic cash ledger affects interest
The proviso to section 50(1) generally limits interest on a delayed section 39 return to the portion of tax paid by debiting the electronic cash ledger, except where proceedings under the specified demand provisions have begun for that period.
Subsequent law and GST Portal enhancements also address qualifying cash already deposited and continuously available in the electronic cash ledger. The portal’s advisory describes a computation using net tax liability reduced by the minimum qualifying electronic cash ledger balance from the due date until debit.
Whether a ledger balance reduces interest depends on the applicable statutory conditions, balance history and portal logic. Preserve the electronic cash ledger extract.
The GST Portal interest calculator
The GST Portal provides interest-calculation assistance within GSTR-3B. Portal advisories explain that the system uses return liabilities, payment breakup and filing information to suggest the interest amount.
A March 2026 advisory introduced re-computation relating to Table 5.1 and qualifying electronic cash ledger balances. Portal-generated values should be reviewed against the return and ledger before acceptance, especially for earlier-period liabilities, part payments or cash deposits made before return filing.
Reconcile differences before filing. Do not overwrite a portal suggestion without retaining a written computation and supporting ledger extracts.
GST interest vs late fee vs penalty
| Charge | Why it arises | How it is measured |
|---|---|---|
| Interest | Tax is paid after the applicable due date | Tax amount, annual rate and delay days. |
| Late fee | A specified return or statement is furnished late | Daily amount subject to applicable limits, notifications and return type. |
| Penalty | A statutory contravention attracts a penalty provision | Depends on the specific default, demand and relief provisions. |
A nil return can attract late fee even when no interest is payable. Conversely, tax reported late can create interest even where a late-fee waiver applies.
Part payments and multiple tax periods
Where tax is discharged in parts, calculate each outstanding balance for the period during which it remained unpaid. Do not apply one end date to the full amount when earlier partial debits reduced the liability.
Split by tax period
Do not combine several months if their due dates differ.
Split by discharge date
Reduce the principal after each valid payment or debit.
Separate tax heads where needed
Reconcile CGST, SGST, IGST and cess with the electronic liability and cash ledgers.
Document earlier-period declarations
Maintain invoice, reconciliation and return evidence where liability is reported later.
Interest on delayed GST refunds
Section 56 addresses interest payable by the government where an ordered refund is not issued within the statutory period from receipt of the application, subject to the provision’s conditions. This is different from interest payable by a taxpayer under section 50.
Do not use this delayed-payment calculator for refund interest because the applicable principal, start date and rate arise under a different provision.
Common calculation mistakes
1. Calculating on gross tax without checking the cash portion
For ordinary delayed GSTR-3B filing, the section 50 proviso is central.
2. Treating the filing date as the payment date automatically
Review the actual electronic cash-ledger debit and portal record.
3. Counting the due date as a delayed day
Delay ordinarily begins after the due date.
4. Ignoring part payments
Recalculate the principal after each valid discharge.
5. Mixing interest with late fee
They arise under different sections.
6. Using 18% for every section 50 issue
Identify whether section 50(1) or section 50(3) applies and verify the notified rate.
7. Ignoring notified extensions or relief
Check notifications applicable to the exact tax period and taxpayer class.
Reconcile the liability before paying interest
TargoLegal can help review the return period, electronic ledgers, part payments and portal calculation and prepare a documented interest reconciliation.
Request GST interest reviewFrequently asked questions
What rate should I select?
18% is commonly used for delayed payment under section 50(1). Confirm the notified rate and provision applicable to the specific default.
Is interest calculated on input tax credit?
For the ordinary delayed-return rule, interest is generally focused on tax discharged through cash, subject to the statutory proviso and exceptions. Wrongly availed and utilised ITC is addressed separately.
Does late filing always create interest?
No. Interest depends on delayed tax payment. A late return with no tax payable may still attract late fee.
How many days should I count?
Generally count from the day after the due date through the date of discharge, subject to extensions and portal computation.
Can cash already deposited reduce interest?
It may, where it satisfies the applicable statutory and portal conditions. Use the minimum qualifying continuous balance, not the highest balance.
Can I rely only on this calculator?
No. Compare the estimate with the GST Portal, electronic ledgers and applicable notifications.
Is late fee included in the result?
No. The calculator estimates interest only.
How do I calculate part payments?
Calculate each outstanding principal separately up to its own discharge date.
Research sources
- India Code — Central Goods and Services Tax Act, 2017, including sections 47, 49, 50 and 56.
- GST Portal — Advisory on Interest Calculator in GSTR-3B.
- GST Portal — Advisory on Interest Collection and related enhancements.
- GST Portal — Advisory on re-computation of interest under Table 5.1, 6 March 2026.
- GST Portal — GSTR-3B filing and interest guidance.
- CBIC — Central Tax notifications for current rates, extensions and relief.
