What's New in FlexiFees: Formula Fees, Per-Weight Rates, Metafield Amounts, Product Categories

Last updated 23 September 2026

The September 2026 release of FlexiFees adds three new ways to calculate a fee and new ways to choose which products pay. You can now write a fee as a formula, charge per kilogram, gram, ounce or pound, and take the amount from a metafield, either per unit (per pouch, per gram) or as a percentage of a stored amount such as a wholesale price. A new product category condition targets whole categories of Shopify’s product taxonomy, and products, collections, countries and states are now picked from lists instead of typed. Everything works on every Shopify plan.

What can I calculate now that I couldn’t before?

FlexiFees now has seven fee types. The four new or extended ones:

They sit next to the existing Fixed, Percentage and Percentage by cost fee types. Every fee type works as a cart fee (one fee line for the whole cart) or a per-product fee (calculated for each matching product and added into one line). The fee types overview compares all seven.

Per weight: any unit, small rates

The weight fee used to charge per kilogram only. Now you pick the unit next to the rate: per kilogram, gram, ounce or pound. Product weights stored in another unit are converted automatically, and rates accept four decimals, such as 0.0125 per gram. As a per-product fee it charges rate × unit weight × quantity; as a cart fee, rate × total cart weight. Weight fees created earlier keep charging per kilogram. See Per weight fees.

Amounts from metafields

Some fees are set per unit of something Shopify has no field for: pouches per can, grams of sugar per bottle, grams of plastic per package. Store that number in a product or variant metafield and Per unit of metafield multiplies it by your rate and the quantity. Percentage of metafield does the same with a percentage, for the classic “40% of the wholesale price” rule when the wholesale price is not your Cost per item. Products without the metafield contribute 0. Details: Per unit of metafield and Percentage of metafield.

Formula fees

When a rule has two parts, a higher-of, or tiers, write it as a formula. A per-product formula can use price, line_total, cost, qty, the unit weight in four units and mf("namespace.key") or pmf("namespace.key") for metafields. A cart formula uses subtotal, subtotal_cost, cart_qty, the cart weight and summed metafields. Functions include min, max, round, ceil, floor, abs and if.

The editor starts you off with templates such as “Whichever is higher” (max(0.65 * qty, 0.02 * price * qty)) and “Percentage of subtotal with a floor” (max(2, 0.03 * subtotal)). It checks the formula as you type and explains errors in plain English. Try it on a real product runs the formula against a product from your store and shows every variable’s value before you save. The formula reference has all variables, functions and eight worked examples.

Choosing products: categories and pickers

• Product category condition. Target products by the Category field on the Shopify product page (Shopify’s Standard Product Taxonomy). Search “beer”, “cosmetics” or “batteries”, and pick from the full path. A parent category covers all its subcategories. It needs the Category field set on your products. Guide.
• Collection picker. Collections are chosen from Shopify’s picker and matched by ID, so renaming a collection no longer breaks a fee. Older title-based conditions keep working and show as “matched by title”.
• Product and variant pickers. Choose products or specific variants with Shopify’s picker and see them as chips with names and thumbnails. Pasting an ID or admin URL still works, up to 1,000 IDs per condition.
• Country and state pickers. Countries and states are picked from lists, stored as Shopify’s codes and shown as names, so typos like “Québec” versus QC are gone.
• Cart total weight in any unit. The weight condition’s threshold can be in kg, g, oz or lb.

The pickers guide covers all of them.

Smaller improvements

• Metafield definitions in a list. Wherever you enter a metafield key, your store’s definitions are offered in a dropdown. A quiet warning appears if a typed key matches no definition, and saving is never blocked. See Metafields in FlexiFees.
• Autocomplete for tags, product types and vendors, from your own catalog, so conditions match the exact spelling.
• Fee changes reach open carts within seconds. Editing, publishing or unpublishing a fee now updates carts that are already open within seconds, instead of up to about three minutes.
• Faster answers from support. FlexiFees now records why a fee did not apply, so support questions are answered faster.

What should I know before using the new fee types?

• Weights must be set. Weight-based fees and conditions read the weight on each variant; a variant without weight counts as 0.
• Metafields must hold numbers. Number, money or unit values such as weight work; empty or text values count as 0. A fee whose total is 0 is not added.
• The first cart with a new amount can take a moment. The first time a newly calculated amount appears, Shopify can take a few seconds, occasionally up to about a minute, to accept the new fee line. FlexiFees retries automatically, and the same amount is instant afterwards. Fixed fees are prepared on save and appear immediately.
• State-based fees need a logged-in customer. The fee is added in the cart, where the state is known only for logged-in customers with a saved address. For guest checkouts the state is only known later, so state-based fees do not apply to guest carts today. A cart-page ship-to-state selector is planned.

What came out of this release?

The release started with a request from a nicotine pouch retailer who needed a percentage of wholesale, a fixed amount per can, a rate per pouch and a rate per ounce, depending on the product. The nicotine and vape fee guide shows that setup. The same tools cover heavy order surcharges by the pound, deposits by product category and e-waste fees by weight or class.