---
title: "How do I limit how many units can be pre-ordered?"
description: "Cap pre-orders per variant or for the whole campaign. How units are counted, what shoppers see at the limit, and how the checkout guard enforces it."
url: "https://smart-preorder.com/help/preorders/preorder-limits"
updated: "2026-11-02"
product: "SMART Preorder & Back in stock"
section: "Help center / Pre-orders"
---


# How do I limit how many units can be pre-ordered?

Open the campaign's **Settings** tab and use **Unit limit**: set the number of pre-order units for **Each variant** (the default for new campaigns) or for **The whole campaign**. When the limit is used up, the Pre-order button hides and checkout refuses more of those units. 0 means unlimited.

## Set a limit

1. Open the campaign and go to the **Settings** tab. **Unit limit** is in the **Checkout** card.
2. Choose **Each variant** or **The whole campaign**.
3. **Each variant:** enter **Pre-order units per variant**. Each variant's Pre-order button hides once that many units of it are pre-ordered. To give some variants their own number, click **Set a different number for some variants**.
4. **The whole campaign:** enter **Limit total pre-order units**. Below the field the app shows how many units are used, for example "12 of 50 units used".
5. Click **Save**.

## How units are counted

- Limits count units (line quantities), not orders. With **Each variant** set to 100 on a product with 3 variants, up to 300 units can be pre-ordered in total.
- Open and fulfilled pre-orders count. Shipping an order doesn't free its units.
- Cancelling a pre-order, or refunding it in full, frees its units.
- Carts reserve nothing: units count once the order is placed.

## What happens at the limit

|  | The whole campaign | Each variant |
| --- | --- | --- |
| Storefront | The Pre-order button hides on every product in the campaign. | Only the full variant stops; the others keep taking pre-orders. |
| Campaign status | **Limit reached**, with the banner "Unit limit reached (50 of 50 units)" in the editor. | Stays **Active**. |
| Sold-out variants | Go back to their own Continue selling setting, so they show Sold out (Notify me can take over if back in stock is on). Variants with stock sell as normal orders. | The same, for the full variant. |
| Shopify Flow | The **Pre-order limit reached** trigger runs. | No trigger. |

To take more pre-orders, raise the limit on the Settings tab and save. The button comes back without waiting.

## The checkout guard

Hiding the button isn't enough on its own: a shopper could have the item in the cart already, or use an old cart link. So the app adds a checkout rule called **Pre-order limit guard** (Shopify admin > Settings > Checkout > Checkout rules). It refuses:

- a pre-order item whose campaign or variant limit is used up: "All pre-orders for [product] have been claimed. Please remove it from your cart."
- more units than are left, adding up every line of the cart: "Only 2 pre-orders left for [product]. Please lower the quantity."
- an item from an inactive or expired campaign: "This pre-order is no longer available. Please remove it from your cart."
- an item from a scheduled campaign until shortly before its start, and mixed carts on campaigns set to **Block**. See [Mixed carts](https://smart-preorder.com/help/preorders/mixed-carts).

> **If the guard isn't there** Shopify allows at most 25 active validation functions per store, across all apps ([Shopify developer docs](https://shopify.dev/docs/api/functions/latest/cart-and-checkout-validation)). If there's no free slot, or the rule is turned off in Checkout rules, checkout doesn't enforce limits and only the storefront does. The app never turns the rule back on for you. The app adds the rule so that, if the rule itself ever fails to run, checkout still goes through rather than blocking your customers.

## See how many units are used

- On the **Pre-orders** page, the **Campaigns** list has a **Units** column, such as "12 of 50 units" or "40 (limit per variant)". It turns red when a whole-campaign limit is reached.
- Click the number to see the units by variant.

## What a limit can't do

- There's no limit per customer or per order. One cart can take every unit that's left, and the same customer can order again until the units run out. A low unit limit is the closest option.
- To sell exactly the stock you have coming in, an alternative is **Only while the product is in stock** in the **Availability** card: set the variant's inventory in Shopify to the number you want to sell, and pre-orders stop at 0.

**Never oversell a pre-order** Per-variant or campaign-wide unit limits, enforced on the storefront and at checkout. Free on the Shopify App Store. [Install SMART Preorder & Back in stock on the Shopify App Store](https://apps.shopify.com/smart-preorder-back-in-stock).

## Frequently asked questions

### Can I limit pre-orders to one per customer?

No. Limits are total units, per variant or for the whole campaign. The checkout guard stops a cart from taking more units than are left, but not a customer from ordering twice.

### Do fulfilled orders free up units?

No. Open and fulfilled pre-orders both count. Only cancelling an order, or refunding it in full, frees its units.

### My Flow workflow on Pre-order limit reached never runs. Why?

That trigger runs only when a whole-campaign limit is used up. With Each variant, the default for new campaigns, a full variant stops on its own and the campaign stays active, so the trigger doesn't run.