Most restaurant owners think bulk buying automatically improves margins, but that's only half the story. Sure, you get better unit prices, but your cost calculations become a nightmare. How do you price dishes made from 10 kilos of fish you bought last week but are only using 2 kilos of today?
The problem with bulk purchasing
Your supplier offers discounts on larger orders. Makes sense to grab those deals, right? But this complicates your cost price calculation:
- You pay today for ingredients you won't use until next week
- Your inventory value rises, but your cash flow drops
- The actual cost price per dish is no longer directly derived from your latest invoice
Result: you're flying blind on what your dishes actually cost.
⚠️ Watch out:
Many entrepreneurs calculate with the old purchase price while they've already bought at a new (higher or lower) price. This completely distorts your margin calculation.
Calculate average purchase price
The solution? Work with a weighted average purchase price. This accounts for different purchase prices and quantities you're juggling.
Formula:
Average purchase price = (Total purchase value of inventory) / (Total quantity in inventory)
💡 Example:
You've purchased salmon at different times:
- Week 1: 5 kg for €18/kg = €90
- Week 2: 8 kg for €16/kg = €128
- Still in inventory: 6 kg
Total purchase value: €90 + €128 = €218
Total purchased: 5 + 8 = 13 kg
Average price: €218 / 13 kg = €16.77/kg
FIFO vs. weighted average
Two approaches to handle bulk inventory:
FIFO (First In, First Out):
- You use the oldest inventory first
- Cost price = price of the oldest batch
- More administration, but more precise
Weighted average:
- All inventory gets the same average price
- Less administration
- Good enough for most kitchens
From years of working in professional kitchens, I've seen restaurants tie themselves in knots trying to track FIFO perfectly. Most find weighted average strikes the right balance between accuracy and sanity.
💡 Comparison example:
You use 2 kg of salmon for dishes this week:
FIFO method: 2 kg at €18/kg = €36 cost price
Weighted average: 2 kg at €16.77/kg = €33.54 cost price
Difference: €2.46 per 2 kg
Impact on your food cost
The method you choose directly impacts your margin calculation:
💡 Practical example:
Salmon fillet on the menu for €24.50 (incl. 9% VAT):
- Selling price excl. VAT: €22.48
- Salmon portion: 180 grams
- FIFO cost price: 0.18 kg × €18/kg = €3.24
- Weighted average: 0.18 kg × €16.77/kg = €3.02
Food cost FIFO: (€3.24 / €22.48) × 100 = 14.4%
Food cost weighted: (€3.02 / €22.48) × 100 = 13.4%
Practical implementation
For daily practice, here's what works:
Weekly:
- Count your inventory per main ingredient
- Calculate the average purchase price
- Update your cost prices in your system
With new delivery:
- Note quantity and price
- Recalculate your average price
- Check if your menu price still makes sense
⚠️ Watch out:
Update your cost prices at least weekly. Supplier prices change more often than you think, and bulk purchases can significantly affect your average price.
Digital vs. manual tracking
These calculations are error-prone if you do them manually. Systems automatically calculate your weighted average purchase prices and update your food cost per dish.
Benefits of digital tracking:
- Automatic recalculation with new deliveries
- Direct impact on your food cost per dish
- Historical overview of price developments
- Less chance of calculation errors
Digital tools handle the math while you focus on cooking.
How do you calculate your margin with bulk purchases? (step by step)
Gather all purchase data
Note the quantity, price per kilo and total amount for each delivery. Do this for all batches still in your inventory. Without this basis, you cannot calculate a reliable average price.
Calculate the weighted average purchase price
Add all purchase amounts together and divide by the total quantity. For example: €90 + €128 = €218 for 13 kg gives €16.77 per kilo. This is your actual cost price for new dishes.
Recalculate your food cost per dish
Use the new average price to recalculate your cost price per portion. Divide this by your selling price excl. VAT and multiply by 100 for your food cost percentage. Check if this still falls within your desired margin.
✨ Pro tip
Recalculate your weighted average every 72 hours during volatile market periods. Price swings of 15% or more can completely throw off your margin calculations if you're not staying on top of them.
Calculate this yourself?
In the KitchenNmbrs app you can do this in just a few clicks. 7 days free, no credit card.
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Frequently asked questions
How often should I recalculate my average purchase price?
With every new delivery and at least weekly. Supplier prices change regularly and bulk discounts can significantly affect your average price. Outdated prices lead to incorrect margin calculations.
What if I buy different qualities of the same product?
Treat different qualities as separate ingredients in your system. Premium salmon and standard salmon have different prices and uses. Don't mix them into one average price.
How do I handle perishable products with bulk purchases?
Factor in a waste percentage in your cost price. If you experience that 10% of your bulk purchase spoils, increase your cost price by 10%. This prevents your margin from being undermined by hidden losses.
Should I include VAT in my purchase price calculation?
No, always calculate your cost prices excl. VAT. Your supplier invoices show prices excl. VAT (VAT is shown separately). This keeps your calculations pure and comparable with your selling prices excl. VAT.
📚 Sources consulted
- EU Verordening 852/2004 — Levensmiddelenhygiëne (2004) — Official source
- EU Verordening 853/2004 — Hygiënevoorschriften voor levensmiddelen van dierlijke oorsprong (2004) — Official source
- EU Verordening 1169/2011 — Voedselinformatie aan consumenten (2011) — Official source
- NVWA — Hygiënecode voor de horeca (2024) — Official source
- NVWA — Allergenen in voedsel (2024) — Official source
- Codex Alimentarius — International Food Standards (2024) — Official source
- FSA — Safer food, better business (HACCP) (2024) — Official source
- BVL — Lebensmittelhygiene (HACCP) (2024) — Official source
- Warenwetbesluit Bereiding en behandeling van levensmiddelen (2024) — Official source
- WHO — Foodborne diseases estimates (2024) — Official source
Food Standards Agency (FSA) — https://www.food.gov.uk
The HACCP standards shown in this application are for informational purposes only. KitchenNmbrs does not guarantee that displayed values are current or complete. Always consult the FSA or your local authority for the latest regulations.
Written by
Jeffrey Smit
Founder & CEO of KitchenNmbrs
Jeffrey Smit built KitchenNmbrs from 8 years of hands-on experience as kitchen manager at 1NUL8 Group in Rotterdam. His mission: give every restaurant owner control over food cost.
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