---
title: "What happens when a cart mixes pre-order and in-stock items?"
description: "What happens when a Shopify cart mixes pre-order and in-stock items: one order, payment, balance, holds, cancelling, and how to warn or block."
url: "https://smart-preorder.com/help/preorders/mixed-carts"
updated: "2026-11-02"
product: "SMART Preorder & Back in stock"
section: "Help center / Pre-orders"
---


# What happens when a cart mixes pre-order and in-stock items?

The cart becomes one Shopify order; the app never splits orders. In-stock items are paid in full at checkout, pre-order items pay their deposit or full price, and any balance is charged later in one go. Per campaign you can **Allow** mixed carts (the default), **Allow, but warn on the product page**, or **Block** them so shoppers check out separately.

## Choose what to allow

1. Open the campaign and go to the **Settings** tab.
2. In the **Checkout** card, find **Mixed carts** and pick **Allow**, **Allow, but warn on the product page** or **Block**.
3. For Warn and Block, edit the **Message** (up to 300 characters). You can translate it on the Design tab under **Translations** (**Mixed cart message**).
4. Click **Save**.

| Option | What the shopper sees | Default message |
| --- | --- | --- |
| **Allow** (default) | Nothing extra. Pre-order and in-stock items check out together. |  |
| **Allow, but warn on the product page** | The message on the product page when the cart already holds in-stock items. | Heads up: your cart mixes pre-order and in-stock items. Pre-order items may ship later. |
| **Block** | The same warning on the product page, and checkout refuses carts that mix this campaign's pre-order items with in-stock items, with your message as the cart and checkout error. | Pre-order items must be checked out separately from in-stock items. |

Two pre-order items from different campaigns in one cart aren't a mixed cart. **Block** relies on the app's checkout rule, **Pre-order limit guard**; if that rule is turned off or Shopify had no free slot for it, only the product page warning works. See [Pre-order limits](https://smart-preorder.com/help/preorders/preorder-limits).

## How a mixed order behaves

| Topic | What happens |
| --- | --- |
| Payment at checkout | In-stock items are paid in full. Each pre-order item pays its campaign's deposit; Shopify adds the deposits together. |
| Balance | One order has one balance due date. With different dates, Shopify uses the earliest; a balance due on fulfillment takes precedence over dates ([Shopify developer docs](https://shopify.dev/docs/apps/build/purchase-options/deferred)). |
| Shipping | If both items share a delivery profile and location, Shopify calculates their shipping together. To price them separately, give the pre-order its own delivery profile ([Shopify developer docs](https://shopify.dev/docs/apps/build/purchase-options/deferred/delivery-and-deferment)). |
| Fulfillment hold | On **On hold** campaigns only the fulfillment orders with a pre-order item are held. In-stock items in their own fulfillment order can ship now. |
| Balance on fulfillment | Charged only when the whole order is fulfilled. Shipping the in-stock items first charges nothing. |
| Cancelling | Shopify cancels whole orders, not single items, so cancelling the pre-order also cancels and refunds the in-stock items. The order page, the bulk cancel dialog and the customer's cancel dialog all say so first. |
| Tags | The order gets the deposit campaign's tags, else the first campaign's. |
| Order page | Lists the other items under **Also in this order (not pre-ordered)** and shows the deposit for the pre-order items only, excluding tax and shipping. |

## Separate checkouts

- **Block** is the way to make shoppers check out pre-orders separately. The app can't split one checkout into two orders.
- Don't use a payment rule that hides every payment method to block mixed carts: it leaves the shopper no way to pay. To hide only some methods when the cart holds a pre-order, see [Payment rule recipes](https://smart-preorder.com/help/payment-rules/payment-rule-recipes).

**Decide how mixed carts check out** Allow, warn or block mixed pre-order carts per campaign, with your own translated message. 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 the app split a mixed cart into two orders?

No. One Shopify checkout is one order. Choose Block on the campaign if pre-orders must be checked out on their own.

### If a customer cancels the pre-order, do they keep the in-stock items?

No. Shopify cancels the whole order, so the in-stock items are cancelled and refunded too. Every cancel dialog in the app and in the customer account says this before it happens.

### Why was the customer charged shipping at checkout on a mixed order?

Shipping depends on your delivery profiles. When the pre-order and in-stock items share a profile and location, Shopify calculates their shipping together at checkout.