What a reordering rule does

A reordering rule sits on a product and says one thing:

Keep at least this much in stock. When it falls below, bring it back up to this level.

Two numbers — a minimum and a maximum. When stock drops under the minimum, Odoo creates a purchase order or a manufacturing order to restore it to the maximum.

That is the whole mechanism. The difficulty is not understanding it. It is choosing the two numbers.

The three fields

Minimum quantity. The trigger. Stock below this and Odoo acts.

Maximum quantity. The target. How much you go back up to.

Multiple quantity. Optional. If your supplier sells in boxes of 24, set this to 24 and Odoo rounds up.

Odoo also needs to know what to do — that comes from the product’s route. Buy creates a purchase order. Manufacture creates a manufacturing order.

A rule with no route does nothing. If your rules are not firing, check the route before anything else.

Choosing the minimum

The minimum must cover demand during your lead time, plus a buffer.

That sentence contains the whole calculation.

Work it out:

Take your average usage per week. Multiply by the lead time in weeks. Add a buffer for the weeks that are busier than average and for the times your supplier is late.

If you use 50 a week and your supplier takes 3 weeks, you consume 150 during the lead time. A minimum of 50 guarantees you run out. A minimum of 200 gives you 150 for the lead time and 50 of buffer.

The most common error is setting a minimum that ignores lead time entirely. It looks reasonable — “keep 50 in stock” — and it produces a stockout every time.

Two things justify a larger buffer:

An unreliable supplier. One who is sometimes ten days late needs more cover than one who is always on time.

Variable demand. If some weeks are three times others, the average is not enough.

Choosing the maximum

The maximum decides how often you order and how much cash sits on the shelf.

Set it high: fewer orders, less admin, possibly better prices — and more money tied up, more space used, more risk if the product stops selling.

Set it low: less cash committed — and constant reordering, more admin, more exposure to a supplier being late.

A practical starting point: enough for four to eight weeks of usage above the minimum. Then adjust based on what actually happens.

Consider your supplier’s terms. If there is a meaningful discount at a quantity, and you will genuinely use it, that may justify a higher maximum. If it will sit for a year, it will not.

Where to use them

Fast-moving, predictable products. Regular usage and a stable pattern. This is where rules work best and where the admin saving is real.

Components you always need. Anything that stops production if it runs out.

Standard stock lines. Products customers expect immediately.

Where not to

Made-to-order products. Use Replenish on Order instead. A reordering rule and Replenish on Order fight each other — one says keep stock, the other says wait for demand.

Slow movers. A product selling three a year does not need automation. Order when you need it.

Anything unpredictable. If usage is driven by a few large irregular orders, a rule based on averages will be wrong in both directions.

New products. No usage history means no basis for the numbers. Set them manually and revisit after a few months.

The review nobody does

Here is the practical point that matters more than the arithmetic.

Rules get set once, during implementation, and are never looked at again.

Demand changes. Suppliers change. Lead times change. Products get discontinued. The rule keeps running with numbers that made sense two years ago.

Review them at least twice a year. Look at:

• Products that stocked out — was the minimum too low?
• Products with far more stock than needed — was the maximum too high?
• Discontinued products with rules still active
• Suppliers whose lead times have changed

This review is often worth more than any forecasting feature. It takes an afternoon and it corrects rules that have been quietly wrong all year.

Multiple locations

If you have more than one warehouse, rules are set per location.

Decide deliberately whether each warehouse replenishes independently from the supplier, or whether one central location holds stock and the others draw from it.

Both work. Setting rules without deciding produces warehouses that order independently when you meant them to share.

Common problems

Rules not firing. Almost always the route. A rule with no Buy or Manufacture route does nothing.

Ordering too often. Minimum and maximum too close together. Widen the gap.

Constant stockouts despite a rule. The minimum does not cover lead-time demand. Recalculate.

Excess stock. Maximum set for demand that no longer exists.

Duplicate orders. Usually a rule on a product that also has Replenish on Order. Remove one.

Checking they work

Do not assume. Test.

Pick one product. Note its current stock. Manually reduce it below the minimum with an inventory adjustment. Run the scheduler.

Did the order appear? For the right quantity? To the right supplier?

Configuration that looks correct and does not fire is common. Finding that on a test is much better than finding it when production stops.

The short version

A reordering rule is two numbers. The minimum must cover demand during the lead time plus a buffer — that is the calculation people skip.

The maximum trades ordering frequency against cash tied up in stock.

Review your rules twice a year. They are set once and forgotten more often than anything else in Odoo, and correcting stale rules is usually worth more than any new feature.