Why add the review interval to lead time?

The next opportunity to order is one review interval away. Stock committed now must cover demand until that next order arrives, so the protection period includes both intervals.

Can inventory position be negative?

Yes. Backorders can exceed usable on-hand stock plus open orders. Enter that negative balance so the replenishment quantity includes the outstanding shortage.

Where do I get the safety stock input?

Use your approved buffer for demand and lead-time uncertainty across the full protection period. This calculator accepts that policy quantity; it does not infer a service level from it.

Should I order early if the shelf is empty?

Investigate the immediate shortage before waiting for this calculation. A late open order increases inventory position but cannot supply today's production; expediting or rescheduling may still be required.

Supply Chain & Procurement calculator

Periodic Review Replenishment Calculator

Calculate the replenishment order due at a scheduled inventory review. Enter demand, the review interval, lead time, safety stock and inventory position from your stock ledger.

What this calculator does

Size the order due at a scheduled review from the protection period, safety stock and current inventory position.

Formula used

Protection days = review interval + replenishment lead time
Protection demand = average daily demand × protection days
Target inventory position = protection demand + safety stock
Order quantity = max(0, target position − current inventory position)
Excess position = max(0, current inventory position − target position)

Inputs explained

Average Daily Demand: Expected consumption per day on your planning calendar.
Review Interval: Days between scheduled purchasing reviews.
Replenishment Lead Time: Days from order placement to usable stock.
Safety Stock: Approved buffer for uncertainty over the full protection period.
Current Inventory Position: Usable on hand plus open orders, minus backorders.

How to use the result

Best suited to weekly supplier ordering, fixed delivery calendar reviews.
Does not calculate service probability, safety stock or supplier pack rounding. Inventory position can mask an imminent shortage when open orders arrive late; inspect receipt dates separately.

Current U.S. benchmarks

U.S. manufacturing runs at 75.7% of capacity (Federal Reserve, Aug 2026). New factory orders are up 8.5% year over year (Census).
USITC reported an average effective tariff statistic — a calculated-duty rate of 12.4% of covered customs value in 2025 across the 57 manufacturing import families MFG Calcs tracks, up from 3.3% the year before. This is a statistical aggregate, not verified cash paid or an entry-specific legal rate. Statutory and effective rates by family are at mfgcalcs.com/tariffs.
Sourcing currencies as of 2026-10-02 (Federal Reserve H.10): 6.7038 CNY and 18.192 MXN per USD. Landed-cost comparisons move with these daily rates.

Common questions

Why add the review interval to lead time? The next opportunity to order is one review interval away. Stock committed now must cover demand until that next order arrives, so the protection period includes both intervals.
Can inventory position be negative? Yes. Backorders can exceed usable on-hand stock plus open orders. Enter that negative balance so the replenishment quantity includes the outstanding shortage.
Where do I get the safety stock input? Use your approved buffer for demand and lead-time uncertainty across the full protection period. This calculator accepts that policy quantity; it does not infer a service level from it.
Should I order early if the shelf is empty? Investigate the immediate shortage before waiting for this calculation. A late open order increases inventory position but cannot supply today's production; expediting or rescheduling may still be required.

Last reviewed 2026-10-12.