What Is Supply Chain Planning?

Supply chain planning is the process of deciding what to make, what to buy, how much of each and when, so that customer demand is met without holding more stock or spending more cash than necessary. It turns a demand forecast into two concrete outputs: a production plan telling the factory what to run, and a purchasing plan telling buyers what to order from which supplier and by which date.

Everything else in the discipline — safety stock, reorder points, S&OP meetings, MRP runs — exists to make those two outputs correct and to keep them correct when reality moves.

The four questions a supply chain plan answers

A plan is only finished when it answers all four:

1. What will we sell? The demand forecast, by product and by period.
2. What must we make? The production plan: which products, what quantity, which week, on which line.
3. What must we buy? The purchasing plan: every raw material and packaging component, in the quantity and on the date needed to support production.
4. What do we do when it goes wrong? The exception plan: which shortage matters, what gets expedited, what gets rescheduled, what the customer is told.

Most planning teams do the first three reasonably well and the fourth badly, because the first three are a monthly exercise and the fourth is a daily one.

A worked example

Take a sauce producer running a 12,000-jar week of tomato ketchup.

The bill of materials says each 1,000 jars needs 24 kg of tomato paste, so the week needs 288 kg. Paste comes in 25 kg sacks, so that is 12 sacks. The supplier’s lead time is 21 days and the minimum order quantity is 40 sacks — a tonne.

That MOQ is the whole problem in one line. Weekly usage is 12 sacks; the smallest order possible is 40. So the real decision is not “do we need paste” but “when does the next tonne have to land, and how much of it will sit in the warehouse for a month”.

Work it backwards:

• Production needs paste in the warehouse by Monday week 6.
• Lead time 21 days, so the purchase order must be placed by Monday week 3.
• Add a week of buffer for a supplier that has confirmed late twice this year, and the order goes out in week 2.
• Current stock is 30 sacks, weekly usage 12, so stock runs out in the middle of week 3.

The plan is therefore: order 40 sacks in week 2, expect them week 5, cover the week-3 gap from the 30 sacks on hand. Now do that for the other 60 line items in the bill of materials, every week, and you have the job.

Where the sub-disciplines fit

The terms overlap and get used loosely. In practice:

• Demand planning produces the forecast — how much the market will take.
• Supply planning decides how to meet that forecast with the capacity, materials and lead times you actually have. See supply planning vs demand planning for where the line sits.
• Production planning and scheduling turns the supply plan into line-level sequences: which SKU runs on which line, in which order, with which changeovers.
• Materials requirements planning (MRP) explodes the production plan through the bill of materials to get gross material requirements, then nets off stock on hand and stock already on order.
• S&OP is the monthly meeting where commercial, operations and finance agree one version of the plan instead of three.

The step-by-step version of how these fit together is in the supply chain planning process.

The three planning horizons

Different decisions need different horizons, and mixing them is a common source of argument in planning meetings.

Strategic, 12–36 months. Capacity, new lines, supplier contracts, which categories to grow. Wrong-level question for a Tuesday morning.

Tactical, 1–12 months. The S&OP horizon. Volume by product family, labour, seasonal build, long-lead-time raw materials. For food producers this is where seasonality bites: if you make Christmas lines, the packaging decision is a July decision.

Operational, 0–6 weeks. The weekly production schedule and the daily purchasing and expediting work. This is where most of the value is won or lost, and it is the horizon that spreadsheets serve worst, because it changes every day.

Why plans go wrong

The failure modes are consistent across manufacturers:

• Stale lead times. The system says 14 days because someone typed 14 days in 2021. The supplier now takes 25. Every plan built on that number is wrong by 11 days, silently.
• Phantom stock. The system says 30 sacks; the warehouse has 22, three of them past their best-before. Planning against book stock rather than usable stock produces shortages that appear the morning of the run.
• The forecast is treated as a target. A forecast is a statement about the future; a target is a statement about ambition. Planning materials against a target inflates stock across every raw material at once.
• Nobody replans. The plan is built on Monday and reality diverges on Tuesday. If replanning takes a day of spreadsheet work, it happens weekly at best, which means you are executing a plan that is on average three days out of date.
• Exceptions are handled in inboxes. The supplier’s “we can only send half” email sits unread, the shortage surfaces at the pre-production check, and the response is a same-day scramble.

What good planning looks like

A well-run planning function tends to share a few traits. The plan is rebuilt on a fixed cadence and after any material change, not when someone gets round to it. Lead times and MOQs are maintained as live data, reviewed against what suppliers actually did, not what they promised. Safety stock is calculated per item from demand variability and lead-time variability, rather than applied as a blanket “two weeks of everything”. And exceptions are worked from a single prioritised list, so the buyer spends the morning on the three shortages that stop a line rather than the thirty emails that arrived.

The measures worth tracking are unglamorous: forecast accuracy at the level you actually plan, supplier on-time-in-full, schedule adherence, stock cover in days by category, and the number of expedited orders per month. The last one is the honest one — expediting is the tax you pay for planning that did not work.

Where software fits

Spreadsheets handle the arithmetic fine. What they cannot do is watch. The MRP arithmetic above takes seconds; noticing at 6am that a confirmed delivery has not been dispatched, that the shortage hits Thursday’s run and that the alternative supplier can cover it if the order goes out today — that is the work, and it is continuous.

That is the specific job Leio does: it connects to your ERP and mailbox, keeps the material plan live against the production schedule, raises and chases purchase orders, and flags the exceptions that actually threaten a run — with the planner deciding, not the software.

If you plan production and purchasing for a food or beverage business, book a demo and we will walk through your own bill of materials and lead times rather than a generic example.