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PAR Level Calculator

Free, in-browser. A periodic-review planning scenario — base demand plus statistical safety stock, with optional decay-rate adjustment for perishables. Nothing leaves your machine.

Units per day. From your POS or recent sales.
Standard deviation of daily observations in the same units.
Days between orders. Weekly = 7.
Days from placing the order to receiving it.
Modeled probability of avoiding a stockout during the protection period.
Optional measured stock loss. Not a food-safety limit.
Used to compute the order recommendation.
Optional fixed cushion on top.
Confirmed incoming units available for this planning period.
Backorders or reserved units, counted only once.
177.4 units
Modeled order-up-to target · safety stock 15.4 · base demand 162
Gap to modeled target: 145.4 units
If your supplier has a pack size, round up to the next pack.
Show the math
Consumption rate18 units/day
Order frequency7 days
Lead time2 days
Protection period (review + lead)9 days
Decay ratenone
Base demand over protection period162 units
Statistical safety stock (z × σ × √9)15.4 units
Manual buffer0 units
PAR level177.4 units
Current on-hand32 units
Inventory position (on hand + incoming − commitments)32 units
Order quantity145.4 units

Periodic-review scenario: protection period = review interval + lead time. Assumes independent daily demand, fixed lead time, and incoming stock that arrives in time. The optional loss model applies proportional loss before daily use; it does not establish food safety or remaining shelf life. Check pack sizes, minimum orders, expiry, and delivery dates before ordering.

The formula

This calculator models an order-up-to target across a protection period:

Target = baseDemand + safetyStock + manualBuffer

Without loss, safety stock is z × σ × √T, where T is review interval plus lead time. With loss fraction d, the same recurrence weights daily uncertainty: safety stock = z × σ × √Σ(1 − d)^(−2k), for days k = 1 through T. Fractional-day inputs use the geometric extension of this model.

For non-perishables, baseDemand is just consumption rate × (review interval + lead time). For optional stock loss (decay rate d > 0), baseDemand integrates the exponential decay of inventory across the protection period:

baseDemand = (c/d) × ((1 − d)^(−T) − 1)
where T = review interval + lead time; c = daily use; d = daily loss fraction

The gap to the modeled target is max(0, target − onHand − incoming + unfilled commitments), using incoming stock expected to arrive in time. The loss model applies loss before daily use. It does not establish food safety or guarantee availability.

How to use this

  1. Pull your average daily sales from your POS for the last 30 days.
  2. Compute the standard deviation of daily sales (Excel: =STDEV.S(...)).
  3. Enter your order frequency and the supplier's lead time.
  4. Choose a cycle-service target based on shortage cost, holding cost, and the validity of the model assumptions.
  5. If using measured stock loss, enter that rate (see how decay rate is defined).

This tool is a standalone planning model. To evaluate connected inventory signals and supplier ordering in LineNow, review your own data and workflow. See pricing for the core plan, optional add-ons, and trial terms.

Related

  • PAR level — the concept
  • Safety stock
  • Decay rate
  • The procurement thesis
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