Do not use a closing balance blindly
A balance visible today does not describe the entire interval. Review the transactions and the amount applicable to the liability being calculated.
GST interest calculator
GST Interest Calculator
Understand the delay. See every rupee.
A head-wise estimate for delayed monthly GSTR-3B. Follow the path from cash tax liability to eligible ledger adjustment, delayed days and interest—without mixing interest with late fees.
Calculate your estimateA four-step path to clarity
Good inputs make the number useful.
- 01
Confirm the period and dates
Choose the tax month and check the due date applicable to your registration. Do not assume the standard date still applies if an extension or relief notification exists. Use the actual or planned filing date on which tax is offset; the due date itself is not a delayed day.
- 02
Separate cash tax from everything else
Review the liability after applicable ITC utilisation. Keep CGST, SGST/UTGST, IGST and cess distinct. Enter zero where a head does not apply. Do not include turnover, invoice value, penalties, late fees or an interest amount already calculated.
- 03
Verify the adjustment, then subtract it once
Use your ledger records to establish the eligible amount for the interval. The calculator subtracts the adjustment you enter from that head’s cash liability. It cannot verify a balance, reconstruct transactions or decide entitlement from a GST number.
- 04
Read the breakdown before you act
Review the number of delayed days and the formula for every tax head. Save the summary if useful, then compare it with your official records. If the facts do not fit the supported scenario, do not force them into these fields.
The important distinctionMoney in the ledger.
Money in the ledger.
Tax actually offset.
These are related events, not interchangeable dates. The calculation needs both the relevant delay and the eligible ledger adjustment.
GSTN’s 2026 enhancement recognises an eligible minimum electronic cash-ledger balance over the due-date-to-offset interval. This tool accepts a verified adjustment; it does not infer one from your current balance.
Do not subtract the same credit twice
The cash-liability input is already after applicable ITC utilisation. The second field is a separate eligible cash-ledger adjustment, not another ITC deduction.
Keep the original evidence
Retain the return, liability breakup and ledger records used to establish your figures. A calculator summary explains arithmetic; it does not replace those records.
Framework: GSTN interest-computation advisory and GST Council January 2026 newsletter.
Follow the arithmetic
One tax head. Ten delayed days.
Illustrative July 2026 return
₹10,000 cash tax, ₹2,000 eligible adjustment.
Assume a confirmed due date of 20 August 2026 and filing with tax offset on 30 August 2026. These dates illustrate the method; they do not establish the deadline for your registration.
Assume the ₹2,000 adjustment has been verified and the other tax heads are zero. No special relief or excluded scenario applies.
- 1 / Count the delay
- 21–30 August = 10 days. The due date is excluded and the offset date is included.
- 2 / Establish the base
- ₹10,000 − ₹2,000 = ₹8,000 subject to interest.
- 3 / Apply the daily calculation
- ₹8,000 × 18% × 10 ÷ 365 = ₹39.45, rounded to two decimals.
- 4 / Keep the result in context
- ₹39.45 is estimated interest only. It does not include the tax itself or any late fee.
Interest calculation background: ICMAI indirect-tax study material. The tool uses simple interest, not compounding.
Three amounts worth separating
Tax, interest and late fee are different.
Tax principal
The underlying tax liability. It forms part of the inputs, but is not added to the estimated interest result.
Interest
The time-based amount estimated on this page. It depends on the supported tax base, delay and rate—not the value of a sale alone.
Late fee
A separate filing-related amount. Even where the estimated interest is zero, review whether a late fee applies.
Explore the late-fee calculatorWhere your GST number fits
A GSTIN identifies the registration—not the interest base.
A business may have multiple GST registrations. Make sure the return, tax month and ledger belong to the same GSTIN before comparing figures. Combining records from different registrations can make an otherwise correct formula meaningless.
Lookup first. Calculate with verified records.
Our GST search can show available registration and filing details. Those records alone do not reveal the complete cash-ledger history or establish eligibility for an interest adjustment. This calculator therefore asks for the inputs directly rather than claiming an automatic GSTIN-based assessment.
Check a GST numberBefore you save the result
Your questions, answered plainly.
Is this different from a GST late-fee calculator?
Yes. This page estimates interest on an adjusted tax base over a period of delay. A late fee relates to delayed filing and follows a different calculation. The interest total here excludes late fees and the underlying tax. Use the separate late-fee calculator when reviewing those costs.
Should I enter my invoice value or total sales?
Neither. Start with the relevant tax payable in cash after applicable input tax credit utilisation. Invoice values can include taxable value and tax together; turnover measures something different again. Entering either as the interest base would produce a misleading result.
Can I deduct today’s entire cash-ledger balance?
No. Check the amount eligible for this liability throughout the relevant interval, not just a current snapshot. Funds deposited later or used elsewhere may not qualify for the full-period adjustment. Enter only the verified applicable amount, separately for each tax head.
Does a challan deposit stop the delay?
Do not treat a deposit date as the offset date automatically. This tool’s supported case uses the date the tax is debited when the return is filed. The separate ledger-adjustment input addresses an eligible balance maintained over the interval. Other payment arrangements need separate review.
What happens if I file on or before the due date?
The calculator returns zero delayed days and zero interest for the entered standard scenario. Dates are checked against the selected tax month. This result does not assess earlier-period tax, other returns or a separate interest liability.
Can I combine balances across CGST, SGST and IGST?
Do not allocate a surplus across heads by assumption. Confirm the applicable ledger position and any permitted transfers before entering an adjustment. The calculator keeps the heads separate and rejects an adjustment larger than the cash tax entered for that head.
Does this cover every GST interest case?
No. The current version supports January–August 2026 monthly GSTR-3B periods with the same period’s supplies and a single tax offset at filing. It excludes QRMP, instalments, prior-period liabilities, special interest relief, assessment proceedings and wrongly availed or utilised ITC. Those cases require different inputs or legal treatment.
Why can my estimate differ from the GST portal?
Check the period, due date, actual offset, liability breakup, eligible ledger adjustment and rounding. This calculator cannot see your ledger or automatically apply a notification. Reconcile differences against the portal’s calculation and current guidance before filing or paying.
Can I save the result without creating an account?
Yes. Calculate first, then choose Print / save PDF and use your browser’s PDF destination. The printable view includes the dates, tax-head breakdown and assumptions. Inputs stay in the page’s memory; refreshing or leaving the page clears them.
Scope and review note. Method reviewed 27 September 2026. This is an informational estimate for the stated scenario, not tax advice, an official portal calculation or an instruction to reduce a declared liability. Check current notifications and seek qualified advice for exceptions. The supported period range is deliberately limited pending further rule review.