Overview

Charge extra for the choices customers make - including three different ways to do this, and choosing the right one depends on how you want the charge to work.

Add-on pricing turns an option from simple information into an additional charge. For example, a customer selects gift wrapping and $3.00 is added to the price, enters an engraving message and $5.00 is added, or chooses a premium fabric with an additional cost.

The app gives you three ways to apply these charges. Choosing the right method from the start can save you a lot of rework. The key difference is whether a real Shopify product is used behind the add-on. This affects inventory tracking, Shopify POS compatibility, and how the add-on appears in the order.

Watch it done — 2:47. Charging for an optional hat on a clothing set, and tracking its stock so you stop selling it once it runs out.

The three ways

Every price field in the app opens the same dialog, which contains these three tabs.

Mode	What it does	Behind the scenes
Existing product	Links to a product and variant you already sell. The add-on costs the same as that variant.	Your own product
New product	You enter a price, and the app creates a product for the add-on.	A product the app creates and manages
Fixed amount	Adds an extra charge to the order. Nothing else is created or linked.	No product at all

Compare them properly

Use this table to choose the right pricing method before you start building.

	Existing product	New product	Fixed amount
Where the price comes from	The linked variant	You type it	You type it
Creates a product in your catalog	No — uses an existing one	Yes	No
Stock can be tracked	Yes	Yes	No
Works with Out of stock options	Yes	Yes	No
Has its own SKU, weight, and tax setting	Yes	Yes	No
Appears as its own cart line	Yes	Yes	No — folded into the main item's price
Can be merged visually with the main item	Yes	Yes	Not applicable
Supported in Shopify POS	Yes	Yes	No
Effort to set up	Medium — you need the product	Low	Lowest
Effort to maintain	Low	Low	None

Which one should I use?

Your add-on is…	Use
A physical thing you already sell — a gift box, a spare part	Existing product
A physical thing you do not sell separately, but need to count — ribbons, boxes, engraving plates	New product
A service with no inventory to track or run out of—such as engraving, expedited production, or a design fee.	Fixed amount
Something you also sell in person through Shopify POS	Either product-backed mode. Not Fixed amount
Something you want reported separately in your Shopify sales reports	Either product-backed mode
Something with different weights that affect shipping	Either product-backed mode

When in doubt, choose New product. It costs nothing extra, gives you stock tracking and POS support if you need them later, and ensures the add-on is included properly in your Shopify reports. Choose Fixed amount only when there is genuinely nothing to track or count.

Pages in this section

Where you can set add-ons

Option level against value level, and which types support which.

Fixed amount directly

The simplest mode, and its one significant limitation.

Existing product

Linking a product and variant you already sell.

New product

What the app creates, how it names the products, and how to keep them out of your storefront.

Advanced add-on modes

All eight quantity modes, each with a worked calculation.

Dimension add-on formula

Calculate the price from measurements the customer enters.

Stock and inventory

Turning on tracking, and what happens when something runs out.

Merge main product and add-ons

Showing add-ons as part of the item rather than separate lines.

Add-on price display settings

How prices are shown on the product page.

How pricing is applied

Why the product page shows a preview while checkout shows the final price.

Limitations

What add-on pricing cannot do, so you know the limitations before you build.

The one thing to understand

The price shown on the product page is a preview, calculated in the customer’s browser. The actual charge is applied by Shopify at checkout.

This is not a workaround—it’s how Shopify works, and it’s what keeps the pricing secure from tampering. It also explains several things that might otherwise seem confusing: why add-on products appear as separate cart lines, why the displayed total can be configured independently, and why customers cannot change the price in their browser.

See How pricing is applied.