Stage 1-4 letters + 18% p.a. interest + GSTIN gates — dunning letter dispatch in under 90 seconds.
| Invoice | Date | Days PD | Amount |
|---|---|---|---|
| INV-0418 | 01 Feb 2026 | 42 | ₹68,200 |
| INV-0431 | 13 Jan 2026 | 61 | ₹52,400 |
| INV-0457 | 26 Dec 2025 | 79 | ₹94,150 |
| INV-0492 | 17 Feb 2026 | 26 | ₹31,800 |
| Total due | ₹2,46,550 | ||
Mid-market AR collections teams chase 150–500 overdue invoices per month with hand-drafted dunning letters in Word. Four error classes silently produce legally defective demand notices and leave interest revenue on the table.
The most common manual error: 18% p.a. interest applied to the full invoice amount rather than the residual balance after partial payments. A demand notice based on inflated interest is legally defective and prejudices any subsequent Section 8 IBC application.
The same softly-worded reminder goes to a 10-day overdue customer and a 75-day overdue customer. Stage 4 legal-referral language never appears; the customer learns the matter has escalated only when the lawyer’s notice arrives weeks later.
Records with no contact email get skipped silently in manual runs — staff move on rather than logging the gap. The customer never receives the letter, the interest clock keeps running, and the limitation period under Section 2(b) of the Limitation Act 1963 may quietly run out.
Source-data integrity issues — an outstanding amount that exceeds the invoice face value, a due date in the future, a structurally invalid GSTIN — produce demand notices that the customer can challenge on first reading. Manual review almost never catches these before dispatch.
Per monthly dunning cycle spent in Word manually drafting, computing interest, and dispatching letters across 200+ overdue invoices. The recomputable interest ledger required by SA 505 (External Confirmations) evidence and the Limitation Act / IBC Section 8 statutory standard is almost never produced.
Dunning letters are evidentiary documents that may be cited in a Section 8 IBC application, an MSME Facilitation Council reference, or an SA 505 external-confirmation audit sample. Four regulatory anchors govern their precision.
The Interest Act 1978 caps contractual interest on commercial debt; CGST Section 50 prescribes 18% p.a. on delayed GST liability. An 18% p.a. ceiling is the market-standard commercial term referenced in vendor MSAs — the workflow computes interest on the residual outstanding, not the invoice face.
For dues to MSME-registered creditors, Section 16 of the MSMED Act 2006 imposes interest at three times the bank rate notified by RBI. The workflow detects MSME-registered receivables and applies the MSMED rate where applicable, distinct from the 18% commercial-rate path.
A dispatched dunning letter and customer reply (or non-reply within the prescribed period) anchor the acknowledgment-of-debt timeline under Section 2(b) of the Limitation Act 1963. A missed letter or unrecorded dispatch event can quietly burn the limitation period.
The Stage 4 legal-referral letter is the statutory demand notice under Section 8 of the Insolvency and Bankruptcy Code 2016. Its dispatch event is the trigger date for Section 9 application timing; the recomputable interest ledger is required evidence at the NCLT.
Seven deterministic passes from AR aging XLSX upload to stage-appropriate dispatched letters with a recomputable interest ledger — in under 90 seconds per run.
Workflow ingests the AR aging register uploaded as Excel with columns for customer name, GSTIN, contact email, invoice number, invoice date, due date, invoice amount, amount outstanding, and currency — mapping directly from Tally Prime, Zoho Books, NetSuite, and SAP exports.
Per-row extraction normalises date formats, strips whitespace, validates currency codes, and standardises GSTIN to uppercase. The composite key of (invoice_number, customer_gstin) is built for downstream stage assignment and interest accrual.
Each row gated on: contact email present, GSTIN 15-char with ‘Z’ at position 14, outstanding ≤ invoice amount, due date in the past, non-zero outstanding, and customer name present. Any FAIL routes to the exception queue, blocking letter generation until corrected.
Records failing any FAIL-severity validation are surfaced in a named exception queue with the specific rule cited — missing contact email (the most common silent failure in manual dunning), corrupted records where outstanding exceeds invoice, or malformed GSTINs.
Days-past-due computed from due date and run date; each invoice assigned to one of four stages: Stage 1 Reminder (1–15 dpd), Stage 2 First Notice (16–30 dpd), Stage 3 Final Demand (31–60 dpd), or Stage 4 Legal Referral (60+ dpd).
Interest computed as (Outstanding × 18%) ÷ 365 × Days Past Due — on the residual outstanding balance after partial payments, NOT the invoice face. Aligns with the rate referenced in MSMED Act Section 16 and the Interest Act 1978 ceiling.
Stage-appropriate letter generated per customer with invoice number, GSTIN, outstanding principal, accrued interest, and total payable. Stage 4 letter includes IBC Section 8 statutory demand notice language. SMTP dispatch + open/reply tracking; Excel export drops into the AR audit workpaper.
The workflow ships with a battery of synthetic test scenarios that exercise every failure mode we have seen in real-world data. Each scenario produces a deterministic outcome that an auditor or controller can verify in seconds.
Seeded sample files used to demonstrate this workflow. Each one exercises a specific scenario or failure mode.
Single-row register for Acme Corp Ltd (GSTIN 27ACMEA1234B1Z5), 10 dpd, Rs 2,85,000 fully outstanding. Demonstrates all four validations passing and Stage 1 Reminder assignment.
Register for Acme Corp with contact_email intentionally blank. Demonstrates the contact_email_required FAIL validation and exception-queue routing.
Register for Acme Corp where amount_outstanding (Rs 42,000) exceeds invoice_amount (Rs 35,000). Demonstrates the outstanding-exceeds-invoice data integrity check.
Register for Acme Corp Pvt Ltd, 22 dpd, partial payment reducing outstanding to Rs 95,000. Demonstrates Stage 2 First Notice letter with interest on the residual balance.
Register for Acme Corp Pvt Ltd, 78 dpd, full Rs 67,500 outstanding. Demonstrates Stage 4 Legal Referral letter generation with 78-day interest accrual.
The Cadel dunning letter generator replaces stage-blind, manually drafted reminder emails with deterministic stage assignment, accurate interest computation on the outstanding balance, and hard data-quality gates — producing a recomputable interest ledger for every dunning run.
(Outstanding × 18%) ÷ 365 × Days Past Due on the residual balance after partial payments — eliminating the most common manual error of accruing interest on the full invoice face value, which produces a legally defective demand notice once part-payment has been received.The questions accountants and finance controllers ask most often before deploying this workflow.
The workflow computes simple interest as (Outstanding Amount × 18%) ÷ 365 × Days Past Due and includes the resulting figure in the dunning letter. An 18% p.a. rate aligns with the ceiling commonly cited in commercial contracts governed by the Interest Act, 1978 and is consistent with the rate referenced in MSME delayed-payment provisions under the MSMED Act, 2006 (Section 16), though the applicable rate for a specific contract depends on its payment terms clause.
The workflow checks that each customer_gstin is exactly 15 characters in length, that the 14th character is the letter 'Z' (the default entity code under the GST registration structure), and that the first two digits represent a valid state code as defined in the CGST Act Schedule. Records that fail this structural check are flagged in the exception queue and excluded from letter dispatch until corrected.
The AR aging register includes a currency column, and the workflow preserves the stated currency on each dunning letter. Interest accrual is calculated on the outstanding balance in the invoice's native currency. For export invoices subject to FEMA regulations, the letter template notes the foreign-currency amount; however, INR conversion for financial reporting purposes must be handled separately per Ind AS 21 using the applicable exchange rate at the reporting date.
Each dunning run produces a timestamped Excel export recording the customer name, invoice number, invoice date, due date, days-past-due, dunning stage assigned, interest amount computed, validation results, and letter-dispatch status. This export can be attached directly to the AR sub-ledger working papers and supports the requirements of ICAI SA 505 (External Confirmations) when auditors request evidence of collection follow-up activity.
Input to the workflow is a standard XLSX-format aged receivables register, which any accounting system — including Tally Prime, Zoho Books, QuickBooks Online, and SAP Business One — can export. The required columns are customer name, invoice number, invoice date, due date, invoice amount, outstanding amount, currency, GSTIN, and contact email. No direct API connector is required; the export-and-upload model keeps the workflow portable across systems without ERP customisation.
The workflow evaluates each invoice row independently and assigns a dunning stage based on that invoice's own days-past-due value. If a single customer appears in both Stage 2 and Stage 4 buckets, two separate letters are generated — one per invoice — each citing the specific invoice number, outstanding amount, and interest accrued. The inbox view groups records by customer with a stage badge on each invoice, making it straightforward for the collections team to review the full exposure before dispatch.
Yes. Letters can be dispatched directly through the integrated SMTP relay (or through SendGrid / Microsoft 365 / Google Workspace where configured) with per-letter open-tracking pixels and reply-detection on the AR mailbox. The collections inbox shows, for each letter, whether it was delivered, opened, replied to, or bounced, and the customer record auto-advances to the next dunning stage if no response is received within the configured response window — typically 7 days for Stage 1 and 3 days for Stage 4.
The Stage 4 legal referral letter template references the company's appointed legal counsel by name and address, includes the statutory demand notice language required under Section 8 of the Insolvency and Bankruptcy Code, 2016 (where applicable to the operational creditor), and attaches the recomputable interest ledger as a schedule. Finance teams can swap the counsel block and adjust the cure-period language through the template console without changing the workflow code, and the workflow records the dispatch event as the trigger date for IBC Section 9 application timing.