Inputs
Example data table
These sample values match the default inputs above, so you can compare quickly.
| Period | Forecast | Firm Orders | Gross Req. |
|---|---|---|---|
| 1 | 180 | 160 | 180 |
| 2 | 210 | 220 | 220 |
| 3 | 240 | 200 | 240 |
| 4 | 200 | 260 | 260 |
| 5 | 260 | 210 | 260 |
| 6 | 230 | 240 | 240 |
Formula used
-
Gross requirements:
GR[t] = max(Forecast[t], Orders[t]) -
Effective demand (when backlog is allowed):
ED[t] = GR[t] + Backlog[t-1] -
Planned MPS quantity (satisfy demand and keep safety stock):
Need[t] = max(0, (ED[t] + SafetyStock) - POH[t-1]), then round to lot size:MPS[t] = ceil(Need[t]/LotSize) * LotSize. If capacity is set, then:MPS[t] = min(MPS[t], Capacity). -
Projected on hand:
POH[t] = max(0, POH[t-1] + MPS[t] - ED[t]) -
Backlog / shortage:
Backlog[t] = max(0, ED[t] - (POH[t-1] + MPS[t])) - Available-to-promise (ATP) at an MPS period: sum firm orders until the next MPS period, then subtract from available supply. This supports customer commit decisions.
How to use this calculator
- Set the planning horizon to match your weekly or monthly buckets.
- Enter beginning inventory and your safety stock target.
- Add forecast and firm orders for each period (comma-separated).
- Choose a lot size and capacity if your line has limits.
- Press Submit to generate the schedule and KPIs.
- Use CSV for spreadsheets, or PDF for sharing the plan.
Planning horizons and time buckets
A practical master production schedule uses consistent time buckets (weekly or monthly) and a horizon long enough to cover your longest critical lead time. In many mid-volume plants, a 6–12 period horizon balances detail and usability. Use shorter buckets for volatile demand and longer buckets for stable lines.
Demand signals and gross requirements
This calculator models gross requirements as the maximum of forecast and firm orders each period. That approach reduces the risk of underbuilding when orders exceed forecast, while still respecting forecast when orders are thin. Track forecast bias and update the forecast weekly to keep gross requirements aligned with reality.
Inventory targets and service protection
Safety stock is treated as a target buffer on top of demand. If projected on hand would fall below the target, the plan triggers production. For example, a 120-unit safety target across a 6-period horizon can protect service during supplier delays, quality holds, or late changeovers. Tune safety stock using service-level goals and variability in demand and supply.
Lot sizing and changeover economics
Lot size rounds planned production upward, reflecting minimum run quantities, packaging constraints, or changeover costs. Larger lots reduce setups but increase inventory and risk of obsolescence. Smaller lots increase responsiveness but can stress capacity. Use this tool to test “what-if” scenarios: 50-unit lots versus 100-unit lots often shift average inventory materially.
Capacity limits and smoothing actions
When a capacity cap is set, planned production cannot exceed that limit in any period. Any unmet demand becomes backlog (or shortage if backlog is disabled). If capacity warnings cluster in specific periods, consider leveling demand, adding overtime, using alternate routing, or pulling work ahead through pre-builds while still honoring safety stock.
Available-to-promise for customer commitments
ATP highlights what you can confidently promise from beginning inventory and scheduled builds after covering firm orders until the next build period. Positive ATP supports confirmed ship dates; negative values signal overcommit risk. Use ATP in weekly S&OP or daily order review to align sales commitments with realistic supply.
FAQs
1) Why does gross requirements use the maximum of forecast and orders?
It prevents underplanning when orders spike above forecast, while still planning to the forecast when orders are light. It’s a conservative, widely used MPS approach.
2) What should I set as a planning horizon?
Choose a horizon that covers your longest cumulative lead time and review cadence. Many teams use 6–12 weekly periods, then roll the plan forward each week.
3) How does lot size affect the schedule?
Lot size rounds planned production up to the nearest multiple, which can increase inventory but reduce changeovers. Smaller lots improve responsiveness but may require more capacity.
4) What does “Backlog allowed” change?
If enabled, unmet demand carries forward and is added to the next period’s effective demand. If disabled, unmet demand is shown as shortage while projected on hand stays non‑negative.
5) Why might ATP be blank in some periods?
ATP is meaningful only at periods that create new availability (beginning inventory and periods with scheduled builds). Other periods don’t introduce new supply to promise.
6) How do I use results in meetings?
Review peaks in gross requirements, capacity flags, and projected on hand. Then compare scenarios (capacity, safety stock, lot size) and export CSV/PDF to share decisions with operations and sales.