Busy store, empty bank account. Your promo doubled sales — so why did your profit disappear? Discounts stack with platform fees, payment fees, shipping, and returns to erase your margin while the dashboard stays green.

Promo Margin Guard is a pre-sale calculator for e-commerce sellers (Shopify, Etsy, marketplaces) who run discounts, coupon codes, and seasonal sales. Enter your price, cost, and planned discount before you launch — it tells you whether the promo will make money or quietly lose it, and exactly how many extra units you'd need just to break even.

The break-even formula: Extra units needed = Discount% ÷ (Margin% − Discount%). Example: a 10% discount on a 40% margin needs about 33% more units just to break even. A 20% discount at the same margin needs 100% more. Most sellers never run that math.

What's inside (file-by-file)

• `Promo-Margin-Guard.xlsx` — 5-sheet Excel workbook (desktop & web, no macros): HOW TO USE, Break-Even Calculator (with 5%–100% stress-test table), True Profit Per Order fee-stack table (30 product rows, your own fee settings), Promo Planner GO / NO-GO verdict (three gates), Post-Promo Audit

• `00-QUICK-START-GUIDE.md` — full onboarding guide: the formula, sheet walkthrough, first-15-minutes plan, honest limits

• `WORKED-EXAMPLE.md` — one complete FICTIONAL promo (candle shop, 20% sale): pre-sale gates, fee-stack cross-check, post-promo audit, lessons. All data labeled EXAMPLE.

• `Discount-Trap-Guide.md` — how discounts train customers to wait, the break-even math behind the trap, and 7 cheaper alternatives (free-shipping threshold, gift with purchase, bundles, loyalty, limited quantity, payment plans, value stacking)

• `Pre-Promo-Checklist.md` — the 12-point checklist to run before every sale

• `DISCOUNT-ALTERNATIVES-WORKSHEET.md` — discount vs. one alternative, side by side, same product

• `FAQ-AND-LIMITS.md` — 10 product-specific FAQs + honest limits

• `WHATS-INSIDE.md` — file-by-file inventory + version history

• `README.md` — package overview + 5-minute quick-start

• `cover.png` + `previews/` — cover and 4 workbook preview images

Total: 14 files.

Free sample (try before you buy)

Read the free sample excerpt before buying — the core formula, one mini worked example, and the checklist excerpt:
https://github.com/fexo9/promo-margin-guard/blob/main/FREE-SAMPLE-Promo-Margin-Guard.md

Demo video

Watch a 72-second walkthrough of the real v2.0 files:
https://youtu.be/G_DcW3QDgyM

FAQ (product-specific)

1. Does it guarantee my promo will be profitable? No. It is a decision tool, not a profit guarantee. It calculates from YOUR numbers. Garbage in, garbage out.

2. What is the break-even formula? Extra units needed = Discount% ÷ (Margin% − Discount%), where Margin% = (Price − COGS) ÷ Price. Standard retail discount math.

3. Why does the Planner use gross profit instead of profit after fees? Deliberate simplification to keep the three gates readable. Fees only make the picture worse — after a GO, always cross-check the fee-stack sheet with your real fees.

4. Fee-stack says LOSS but Planner says GO — which do I trust? The fee-stack sheet. It includes fees; the Planner does not. Fix the price, fees, or product list, then re-run.

5. What if my discount equals or exceeds my margin? Stop. Every unit loses money; no volume fixes it. The workbook says DANGER / INVALID instead of dividing by zero.

6. What uplift should I enter? Your honest estimate from past promos — ideally your Post-Promo Audit actuals. An optimistic uplift is the most common way a NO-GO becomes a launched losing promo.

7. Does it work for services or digital products? Yes — enter your price and true per-unit cost. For subscriptions, use per-billing-period numbers.

8. Does it work in Google Sheets? It opens and calculates, but layout was designed and tested for Excel (desktop & web). Standard formulas only — no macros, no add-ins.

9. What if I see "CHECK INPUTS"? A yellow input is blank or invalid. Fill the yellow inputs; formulas never show raw error cells.

10. Multiple channels with different fees? Run the fee-stack sheet once per channel, or use the higher-fee channel to be conservative. Do not average fees — the average hides the channel that loses money.

Honest limits

• Not a profit guarantee. It calculates from your inputs.

• Planner gates use gross profit (before fees). Always cross-check the fee-stack sheet.

• Uplift is an estimate — base it on audit actuals, not hope.

• Sample data is fictional. Fee defaults are examples only — enter your platform's actual fees.

• No tax or accounting advice. No chargeback modeling beyond the flat return-rate reserve.

• Excel-first; Google Sheets "opens and calculates," not pixel-perfect layout.

• No sales, review, or testimonial claims.

Details

• Price: $24 one-time. Commercial license.

• Format: ZIP download (14 files: Excel workbook + Markdown docs + cover + previews). Excel desktop & web; no macros.

• Version: v2.0 (2026-10-17). Changelog: added quick-start guide, worked example, FAQ + limits, inventory, alternatives worksheet, HOW TO USE sheet. Price unchanged.

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