How to get the most from MRP in Microsoft Dynamics GP

Imagine, for a moment, that your material requirements planning (MRP) system generates a perfectly time-phased plan. Procurement acts on it without a second thought. Production hits every date. The inventory sits exactly where it should—no more, no less. It sounds like fantasy, but it doesn't have to be. The catch is that configuration, data and governance must work in concert, each one reinforcing the others.

MRP in Microsoft Dynamics GP is a powerful engine, one built to turn demand signals into clear buy-and-make actions. But when any of those three pillars wobble, the noise grows. Decisions stall. Confidence quietly erodes. And supply chain teams—who already have plenty of noise to contend with—find themselves right back where they started: guessing instead of planning.

This article distills key insights from RSM's webinar, “MRP in Dynamics GP: Plan, predict and prosper,” presented by Steve Connors and Audra Beers. Think of it as a practical roadmap—one that walks you through setting up, running and continuously improving MRP so your organization can reduce surprises, strengthen promise dates and keep inventories lean.

MRP fundamentals: How the engine works

At its core, MRP performs a straightforward calculation. It nets gross demand—sales orders, forecasts and bill of materials component requirements—against gross supply, which includes on-hand inventory, open purchase orders, open manufacturing orders and approved returns. It does this across defined time buckets. Whenever demand exceeds supply in any given bucket, the system responds by generating planned purchase orders, planned manufacturing orders, or suggestions to reschedule and cancel. The concept is simple. The execution, however, is where nuance lives.

Order policies control how those shortages become recommendations, and choosing the right one matters more than most teams realize:

• Lot-for-lot: Aligns supply directly to dated requirements, matching each need with a corresponding order.
• Period order quantity (POQ): Groups needs over a defined time horizon, consolidating demand into fewer, larger orders.
• Fixed order quantity (FOQ): Uses standard lot sizes driven by cost, capacity or vendor rules, creating predictable order patterns.
• Not planned: Excludes noncritical items from the process entirely—because nobody needs MRP telling them when to order sticky notes.

Assign these policies at the item-site level with clear intent. They shape the plan's behavior and responsiveness, and a careless assignment can ripple through the entire supply chain.

Configuration essentials: Item-site setup, vendor data and item metrics

Item resource planning at the item-site level is where the real governance begins. It controls planning status, default site, replenishment method—whether an item is bought, made or both—and order policy. Most settings inherit from site defaults, which is convenient, but you should override them wherever business rules differ.

One setting deserves particular attention: confirm that “Calculate MRP for this item-site” is enabled for every planned item. Items left unselected stay invisible to the system—out of sight, out of plan and potentially out of stock.

Accuracy in make, buy and dual-source classifications is equally critical. A wrong classification generates the wrong type of recommendation and sends teams confidently down the wrong path. That outcome is arguably worse than no recommendation at all, because at least silence invites questions. Manage exclusions with the same deliberateness. Items, sites and item-site combinations can be excluded in several ways, and new setups often create unintended gaps that leave critical SKUs quietly unplanned.

Each item-site should link to the correct primary vendor, complete with accurate lead times, order multiples, minimum and maximum quantities, and vendor item numbers. When these details are right, MRP handles rounding, packaging and minimums automatically, freeing buyers to make decisions instead of redoing arithmetic.

Safety stock, reorder points and minimum/maximum levels need to align with service targets and demand variability. Set them too low, and stockouts follow. Set them too high, and capital sits tied up on shelves. Neither scenario wins friends in the executive suite. Confirm that default sites and receiving calendars reflect reality so promise dates actually mean something.

Here is the key relationship to remember: item metrics determine when to replenish, while vendor metrics define how. If either is off, suggestions require constant rework—and nothing kills trust in a system faster than suggestions no one follows.

Establishing a disciplined MRP cadence

Consistency is the foundation of trust, and MRP is no different. Run regenerations daily for fast-moving items, weekly or on a longer cycle for stable portfolios, and fix the timing so teams know exactly when to expect fresh output. Predictability breeds trust. Ambiguity breeds workarounds. Workarounds breed spreadsheets. And before long, your enterprise resource planning system is little more than a spectator.

Use preferences to surface inactive items for portfolio oversight without pulling them into active calculations. Take the time to verify available-to-promise (ATP) and time-phased inquiry behavior—specifically, how past-due orders are handled, how pegging is assigned and how netting is applied across buckets.

Treat MRP output not as a list of tasks but as a prioritized decision queue:

• Plan orders that align with policy and constraints.
• Reschedule when pegging and downstream impact justify the change.
• Cancel only after cross-functional alignment—because a cancelled order may solve one problem while creating three more.

Track recurring exceptions to uncover their root causes, whether those turn out to be inaccurate lead times, unsuitable order policies, incorrect routings or bill of materials (BOMs), or supplier constraints. Fix them quickly so both the system and the process continuously improve.

Set past-due and forward-looking days to match real replenishment cycles. Overly long horizons increase runtime and distort priorities. Decide whether back orders count as firm demand and document the policy clearly. Standardize time buckets and naming conventions so every reviewer works from common definitions. When everyone reads the same sheet of music, the plan holds. When they don't, meetings get longer and progress gets shorter.

Regeneration methods and controls

Two regeneration methods serve different purposes, and knowing when to use each one keeps the process efficient:

• Full regeneration: Is best suited for baseline runs and for use after significant changes to policies, lead times, structures or calendars.
• Net regeneration: Works well for intraday or interim runs, capturing deltas while managing compute time.

Purchase request resolution offers another efficiency lever. Use it to consolidate demand and reduce purchase order (PO) proliferation by adding lines to existing POs where practical. Your vendors will thank you—or at least stop asking why they received four separate POs in a single afternoon.

Review exclusions at the item, site and item-site levels on a regular basis. Rebuild after adding items or sites so the plan reflects your current operational footprint. Keep an eye on MRP security locks, too; they can cause phantom “in-use” errors. Intervene only after confirming that no valid process is running.

Inquiry tools that turn data into decisions

The real value of MRP emerges not just in generating recommendations but in providing the tools to interrogate them. The inquiry suite translates raw calculations into accountable actions:

• Quantities query: Offers reusable filters by item, site, date and document type; build the query once and use it every cycle.
• Pegging inquiry: Connects each recommendation to its source demand—whether that is a sales order, a forecast or a parent manufacturing order—so you can confirm impact before acting; knowing the “why” behind a suggestion is the difference between acting on data and acting on faith.
• Workbench: Provides a time-phased view of demand, supply and projected balances, making it possible to spot coverage gaps early—before they become someone's emergency.
• Projected available balance  inquiry: Enables what-if scenarios for demand surges or supplier delays, allowing you to stress-test the plan before committing resources.
• Focused views: Round out the suite: MRP view for summaries, item inquiry for single-SKU detail, plus order windows for sales, purchase, manufacturing and pick lists.

Together, these tools help teams act promptly, confidently and with a clear audit trail.

Data rigor: Sustaining MRP performance

A planning system is only as good as what you feed it—and this one has a long memory for bad data. Maintaining data quality is not a one-time task but an ongoing discipline that spans several domains:

• Engineering data: Accurate bills of materials and routings, complete with effectivity dates, yield and scrap factors and component planning flags, all aligned to real production conditions.
• Lead times: Set from measured actuals, not aspirational targets; update them after any change to suppliers, processes or the distribution network.
• Calendars and constraints: Receiving, production and vendor calendars must reflect shutdowns, holidays and capacity limits; MRP cannot plan around a shutdown it does not know about.
• Service targets: Item-level service classes should align with demand variability, supplier reliability, margin and strategic importance.
• Accountability: Establish clear data-domain ownership; track metrics that matter: expedite rate, plan adherence, exception aging, on-time delivery, inventory turns and working capital utilization.
• Review cycle: Follow a standardized post-regeneration sequence—review exceptions, address urgent shortages, resolve due-date misalignments, identify release and cancel candidates—with every decision recorded for transparency.
  

Common failure modes—and how to fix them

Knowing what can go wrong is half the battle. Fixing it before someone notices is the other half. Here are the most frequent culprits and their remedies:

• No planned orders for critical SKUs: The item-site is not set to planned, the default site is wrong or an exclusion is active. Correct the flags, verify the replenishment method and check the item-site linkage.
• Wrong supply type (PO vs. MO): The make/buy classification is incorrect. Update the engineering data and item resource planning settings to reflect reality.
• Chronic expedites: Lead times are too short, suppliers are unreliable or safety stock is too low. Adjust lead times from historical data and recalibrate buffers. If every order is urgent, then no order truly is—and your buyers are just firefighters with purchase cards.
• Excessive small orders: Lot-for-lot is being used where POQ or FOQ would be a better fit, or vendor multiples are missing. Consolidate ordering with POQ or FOQ and maintain vendor minimums.
• MRP “noise”: Misaligned buckets, differing user preferences or overly broad planning horizons are clouding the output. Standardize displays and refocus exception management.
• Past-due congestion: Stale open orders are clogging the queue. Clean them up, close or cancel them and enforce disciplined posting going forward.