What PromoMath does
PromoMath checks whether a sale you are thinking about will still make money. You pick the products, enter the discount you have in mind, and set the lowest gross margin you are willing to accept. PromoMath reads the price and Cost per item already saved in Shopify and tells you, variant by variant, which ones are safe to discount, which fall below your margin, and which would sell below cost.
It is a planning tool. It does not change prices, create discounts, move inventory, or publish anything to your store. It is not accounting software and it is not a profit report on past orders.
How to run an analysis
- Open PromoMath from the Apps section of your Shopify admin.
- Choose what you are considering discounting: all products, one collection, or specific products.
- Enter the proposed discount as a percentage, for example 20 for 20 percent off.
- Enter the minimum gross margin you want to keep, for example 30 for 30 percent. PromoMath remembers this number for next time.
- Run the analysis. Each variant is sorted into Safe, Low Margin, Losing Money, or Missing Cost, with its maximum safe discount where one can be worked out.
- Export the results to CSV if you want to work through them in a spreadsheet or share them with whoever does your buying.
Why Cost per item is required
Margin is the gap between what you sell an item for and what it costs you. Without a cost there is nothing to compare the sale price against, so PromoMath cannot say whether a discount is safe. Shopify keeps that number in a field called Cost per item on each variant.
To set it: in your Shopify admin go to Products, open the product, open the variant, and find Cost per item under Pricing. Enter what you pay for the item and save. If you have many variants to fill in, Shopify's bulk editor lets you set cost for a whole list at once. Run the analysis again afterwards.
What margin means here
PromoMath uses gross margin on the discounted price: the sale price minus Cost per item, divided by the sale price. A $40 item that costs you $10 has a 75 percent margin at full price. At 20 percent off it sells for $32, so the margin drops to about 69 percent. Shipping, payment fees, duties, returns, and labor are not included unless you have built them into your Cost per item.
What each result means
- Safe. At the proposed discount, the variant stays at or above your minimum margin.
- Low Margin. The variant still makes money at the proposed discount, but its margin falls below the minimum you set.
- Losing Money. The sale price would be below the variant's Cost per item. Every unit sold at this discount loses money.
- Missing Cost. Shopify has no Cost per item for the variant, so margin cannot be calculated. The variant is flagged rather than counted as safe. A variant is also marked Missing Cost when its price is blank or its cost is saved in a currency different from your store's default currency.
Maximum safe discount
For every variant with a price and a cost, PromoMath also works out the deepest discount that still holds your minimum margin. If your floor is 30 percent and a variant can take 42 percent off before it drops below that, its maximum safe discount is 42 percent. Use it to find the variants that can carry a bigger promotion, and the ones that cannot. The number is rounded down, so the value shown is always on the safe side.
Troubleshooting
Most of my variants say Missing Cost
Cost per item is empty on those variants in Shopify. Fill it in as described above and run the analysis again. Variants with no real cost, such as a digital download, can be left blank and skipped.
A product I expected is not in the results
PromoMath only looks at active products, and it skips gift cards. Draft and archived products are not for sale, so discounting them changes nothing. A gift card has no meaningful Cost per item, so any margin shown for one would be wrong.
The numbers are in the wrong currency
All amounts are shown in your store's default currency, because that is the currency Shopify saves prices and costs in. Prices shown to shoppers in other markets can differ. A cost saved in another currency is marked Missing Cost rather than converted at a guessed rate.
The analysis will not run on a large selection
Very large catalogs can exceed what PromoMath checks in one pass. Pick a collection or a shorter list of specific products and run it again.
The app asks me to pick a plan
PromoMath needs an active subscription or trial. Shopify shows the plan page the first time you open the app; approving it starts the free trial. If you already approved a plan and still see this page, email support with your store domain.
Billing
PromoMath costs $9/month with a 7-day free trial. Shopify bills the subscription and it appears on your regular Shopify invoice. You are not charged during the trial. To cancel, uninstall PromoMath from your Shopify admin; Shopify stops the subscription at that point. Refunds follow Shopify's own app billing rules.
How to get support
Email james@jamesmckinney.xyz. To get an answer on the first reply, include:
- Your store domain, for example my-shop.myshopify.com
- What you were trying to do
- What happened instead, and any message you saw on screen
- The discount and minimum margin you had entered
- A screenshot, if the problem is something you can see
Never send passwords or staff account details. PromoMath does not need them and support will never ask for them.
Privacy and terms
Read the PromoMath Privacy Policy or the PromoMath Terms of Service.