Ingredient prices fluctuate constantly. Calculate weighted averages based on purchase quantities and values over 4-8 weeks to get stable cost prices for menu planning.
Ingredient costs bounce around more than a pinball these days. Your beef supplier charges €8/kg one week, then €9.50 the next. You need one solid average price to build your cost calculations around.
Why calculate an average purchase price?
You can't redesign your menu every time salmon prices jump. Customers would think they're dining at a commodity exchange instead of your restaurant. Stable cost prices help you calculate food costs accurately and set menu prices that actually make sense.
But which price do you pick? Yesterday's delivery? Last month's numbers? Your gut feeling?
- Average too low → your food cost percentage looks better than it really is
- Average too high → you'll price customers right out the door
- No system → you're guessing at profitability
The weighted average method
A weighted average crushes simple arithmetic every single time. You don't just add prices together - you account for how much you actually bought at each price point. After managing kitchen operations for nearly a decade, I can tell you this approach saves restaurants from nasty surprises come month-end.
💡 Example:
Your salmon purchases over 4 weeks:
- Week 1: 5 kg at €22/kg = €110
- Week 2: 3 kg at €24/kg = €72
- Week 3: 8 kg at €21/kg = €168
- Week 4: 4 kg at €25/kg = €100
Total: 20 kg for €450
Weighted average: €450 ÷ 20 kg = €22.50/kg
Compare that to the simple average of (€22 + €24 + €21 + €25) ÷ 4 = €23/kg. The weighted version reflects reality better because you bought twice as much during that cheaper week 3.
Weighted average formula
Weighted average price = Total purchase value ÷ Total quantity
Where:
- Total purchase value = sum of (quantity × price) for each purchase
- Total quantity = sum of all quantities purchased
⚠️ Note:
Keep your units consistent. Don't mix kilograms with pounds or individual pieces.
What period should you use?
Most ingredients work well with 4-8 weeks of purchase data. That's long enough to iron out random price bumps but short enough to catch real market movements.
- Fresh products (fish, meat): 4-6 weeks
- Pantry staples (rice, pasta): 8-12 weeks
- Seasonal items: current season only
💡 Seasonal example:
Asparagus in March: €18/kg
Asparagus in May: €8/kg
For your summer menu, stick with May prices only. Don't average March through May.
How often to update?
Refresh your averages every 2-4 weeks, depending on how often you order and how crazy the market gets.
- Frequent orders (2-3x weekly): update every 2 weeks
- Weekly orders: update every 4 weeks
- Volatile markets: check more frequently
Track digitally
Spreadsheets work great until they become a nightmare. After a few months, you'll have a tangled mess of numbers that nobody wants to touch.
Digital tracking perks:
- Automatic weighted calculations
- Direct integration with cost prices
- Price trend history
- Alerts for significant changes
💡 Impact example:
You use 200 grams of salmon per portion.
Previous average: €20/kg → €4.00 per portion
Updated average: €22.50/kg → €4.50 per portion
Difference: €0.50 per portion. At 100 portions monthly = €50 impact on costs.
How do you calculate a weighted average purchase price?
Gather your purchase data
Note from the last 4-8 weeks: date, quantity, price per kg/unit, and total amount per purchase. Track one product at a time, for example beef or salmon only.
Calculate the totals
Add up all quantities (total kg) and all amounts (total euros). Check: total amount must match the sum of (quantity × price) per purchase.
Divide total amount by total quantity
Weighted average = total euros / total kg. This is your new average purchase price. Update this price in your cost price calculations for all dishes with this ingredient.
✨ Pro tip
Calculate weighted averages for at least 10-12 weeks before making major menu price adjustments. This timeline separates temporary market hiccups from real cost trends that'll stick around.
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Frequently asked questions
Should I include VAT in the average price?
Skip the VAT when calculating averages. Your supplier invoices show pre-VAT prices, so use those numbers for your cost calculations.
What if I only order once monthly?
Use your last 3-4 purchase occasions instead of a time period. You need enough data points, regardless of how much time passes between orders.
How do I handle products with multiple suppliers?
Calculate separate averages for each supplier, then weight by purchase volume. If Supplier A provides 70% of your tomatoes, their price should dominate your overall average.
What if prices suddenly spike 30%?
First, double-check it's not an invoice mistake. If the increase is legit, update your average right away and think about adjusting menu prices.
Can I just use my most recent purchase price?
You could, but you'll panic over every little price bump. A weighted average smooths out the noise and shows you what costs really look like.
How do I handle partial deliveries at different prices?
Treat each delivery as a separate purchase, even if it's the same order. If Monday's beef costs €12/kg and Wednesday's costs €13/kg, calculate them separately in your weighted average.
What about products I buy in different package sizes?
Convert everything to the same unit first. If you buy 5kg boxes one week and 10kg cases the next, calculate per kilogram for both before averaging.
📚 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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