Reservation of Inventory in SAP MB21, MB1A, MBST, MB22

By : Olivia Turner Olivia Turner
Hours Updated

⚡ Smart Summary

Reservation of Inventory in SAP MM locks stock in advance for a cost center, production order, or stock transfer using MB21, then processes issues with MB1A, reversals with MBST, and closure with MB22.

  • 🔘 Purpose: Reservations block quantities in MRP/ATP so a later document cannot consume the same stock unexpectedly.
  • ☑️ MB21: Create the reservation manually — pick movement type 201 for cost center, 261 for production order, or 311 for stock transfer.
  • ✅ MB1A: Post the goods issue referencing the reservation number, adjust quantity or storage location, then save to get the material document.
  • 🧪 MBST: Reverse the posted material document — SAP applies the reversal movement type (202 for a 201 issue) defined in OMJJ.
  • 🛠️ MB22: Close a reservation for good by ticking the completed flag so it no longer participates in availability checks.
  • 🤖 AI Assist: Copilot and AI-driven MM tools automate reservation creation from demand signals and flag stale reservations before they distort MRP.
Read More

Reservation of Inventory in SAP MM

Reservation of Inventory in SAP

Reservations are system documents that signal a requirement for a certain quantity of a material for production, a cost center, or any other need.

Reservations matter in planning, MRP, and ATP because SAP earmarks the required quantities before they are posted. Without reservations, a production order might need materials that a sales order picked up minutes earlier. When you create a reservation, SAP blocks any other document from consuming that quantity for a different purpose. This behavior depends on the system settings for MRP and ATP. You can give reservations priority to always draw stock even when reserved by a sales order or delivery (not a clean solution), or configure sales orders to skip the reservation during availability checks.

You can create a reservation for a material for many reasons. The system can also create the reservation automatically if the MRP settings imply that behavior.

This is done either automatically by the system or manually using the MB21 transaction code.

Reservation of Inventory by using MB21

Step 1)

1. Execute transaction MB21.
2. Fill in the fields as needed.

Reservation of Inventory in SAP MB21 initial screen

A reservation can be posted for consumption at a cost center (movement type 201), a production order (movement type 261), a stock transfer (311), a sales order, a project, a network, and so on.

Choose the appropriate movement type. For this tutorial choose movement type 201.

If you enter movement type 321, SAP throws an error message because that movement type cannot create a reservation.

Step 2)

1. Enter the cost center.
2. Fill in the item data — material number, quantity, and source storage location.

Reservation of Inventory in SAP MB21 item data

Save the document. SAP returns a reservation number that you use in the next step.

Reservation number confirmation in SAP MB21

Now create a material document for the reservation. You can do that through MIGO, but this section covers another transaction.

Reservation of Inventory by using MB1A

Use transaction code MB1A to post a goods issue with reference to the material reservation.

Step 1)

1. Execute the transaction.
2. Choose the To Reservation… button.

Reservation of Inventory by using MB1A — To Reservation button

Step 2)

1. Enter the reservation number.
2. Confirm.

Reservation of Inventory by using MB1A — enter reservation number

Step 3)

1. Adjust any field — quantity, storage location, and so on — and save the document.

Reservation of Inventory by using MB1A — save document

SAP returns the material document number in the status bar message.

Reservation of Inventory by using MB1A — material document number

If the reservation needs to be reversed, use MIGO or the transaction covered next.

RELATED ARTICLES

Reservation of Inventory by using MBST

Step 1)

1. Execute the MBST transaction code.
2. Enter the document number created in the previous step and press ENTER.

Reservation of Inventory by using MBST — enter document number

Step 2) SAP uses movement type 202 for this purpose — the reversal for a cost-center issue.

That mapping is set up in OMJJ, which defines 202 as the reversal movement type for 201.

Save the transaction data and the previous document is reversed.

Reservation of Inventory by using MBST — reversal saved

Now you can create a material document for the same reservation again, or close the reservation itself using t-code MB22.

Reservation of Inventory by using MB22

Step 1)

1. Execute the transaction.
2. Enter the reservation number and press ENTER.

Reservation of Inventory by using MB22 — enter reservation number

Step 2) Tick the check box to mark the reservation completed (SAP will not expect further goods postings on this reservation).

Reservation of Inventory by using MB22 — mark completed

The reservation is now dismissed from further processing.

FAQs

A reservation is an SAP MM document that earmarks a specified material quantity for a future goods movement — such as a production order, cost center, or stock transfer — so MRP and availability checks respect that commitment.

Common types are 201 (cost center), 261 (production order), 311 (stock transfer within plant), plus 202 and 262 as their reversals. Choose the type that matches the receiving object; SAP blocks incompatible types like 321 at MB21.

SAP stores reservation headers in table RKPF and reservation items in table RESB. Reports like MB25 read these tables to list open reservations by material, plant, cost center, or production order.

MBST reverses a posted material document (undoes the goods movement) using the reversal movement type from OMJJ. MB22 changes the reservation itself — typically ticking the completed flag so no further postings are expected.

Yes. Reservations create dependent demand that MRP includes when calculating requirements, and ATP subtracts open reservation quantities from available stock. Customizing controls whether sales orders check reservations during availability checks.

Transaction MB25 (program RM07RESL) lists reservations by plant, material, cost center, or account assignment. It shows open, completed, and released status so planners can clean up stale reservations before month-end.

AI-driven MM analytics detect reservations that never converted to a goods issue, flag duplicate reservations for the same demand, and recommend closure so MRP stops locking phantom stock. Machine-learning models forecast reservation demand from historical patterns.

Copilot for SAP can draft BAPI_RESERVATION_CREATE1 calls or GUI-scripting steps for MB21 from a plain-English demand list, mapping material, quantity, cost center, and movement type. Consultants review the script before it runs against production.

Summarize this post with: