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Every morning a kitchen makes the same decision without ever doing the arithmetic: how many portions of the special do we prep? Too few and you send margin out of the door. Too many and you bin food. Almost everybody picks the average — which is precisely the number you know will be short half of the time.
There is a calculation for this decision, it is almost eighty years old, and hospitality never makes it. It comes from operations research, where it is called the newsvendor problem: you buy a stack of papers in the morning, you do not know how many you will sell, and at six o'clock whatever is left is worth nothing. A daily special, a fresh fish, a pot of soup and a tray of cut vegetables are exactly the same problem.
What the calculation shows is uncomfortable. The right number is almost never the average, it sits structurally above it, and it means throwing something away more often than you do now. Not because waste does not matter, but because one portion short costs most kitchens three to four times more than one portion spare — and while those two amounts sit that far apart, being careful is the most expensive option on the table.
This guide walks the four numbers that decide the answer: what one portion short costs, what one portion spare costs, what percentage those two produce together, and how that percentage becomes a number of portions. At the bottom you put your own dish into the calculator and see, in euros a year, what your current number is costing you.
After that come three levers that change the answer without touching your forecast at all — including the only one that brings your sell-outs and your waste down together. Everything computes in your own browser: nothing is sent and nothing is stored.
Why "average" means: short on one service in two
Ask a cook how many portions of the special are prepped and the answer is an average: we usually do about twenty-four. That is a perfectly reasonable answer to the question "how many do we normally sell". It is simply not an answer to "how many should we prep", and the gap between those two questions is where the money is.
An average is by definition the middle. If you prep exactly the average, then on roughly half of your services demand is higher than what is standing there. So you sell out on one service in two. In a place running five services a week that is two or three times a week a guest choosing something else, a floor saying "that's gone" at a quarter to eight, and a cook filing it under careful planning.
The opposite instinct exists too, and it is just as ungrounded: kitchens that habitually prep generously because selling out is "not an option". Both attitudes are a gut feeling about risk, not a calculation. The calculation below turns that gut feeling into a figure, and the pleasing part is that the figure comes out differently per dish — on one it agrees with you, on the next it does not.
The ultimate guide Menu Engineering & Drinks: 6 Steps to More Margin From menu layout to drinks margin: everything your menu can earn you, in one guide. Open the guideThe four numbers, one at a time
Each number adds exactly one thing, and after each one the answer visibly moves. You need no till system to find them — three are already in your recipe costings, and the fourth you count in a fortnight.
1. What one portion short costs you
Ask what it costs to come up one short and the first answer is almost always the menu price. The special is €20.50, so you are out €20.50. That is wrong: the guest never had that plate, so you never spent the ingredients either. What you missed is not the revenue but the margin — what that plate would have left behind in the business.
And that is still not the figure on your menu. European menu prices are VAT-inclusive, and VAT is the state's money passing through your till. At 13.5% VAT, €20.50 on the menu is €18.06 of revenue. Take off the €5.45 of ingredients and you are left with €12.61. That is what one portion short costs.
It sounds like hair-splitting, and on a fat-margin dish it nearly is: work on the gross price and you overstate this number by a few per cent. On a thin-margin dish — fresh fish, shellfish, anything where purchase price is a third of the menu price — that same error grows to several portions' difference in the final advice. Exactly on the dish where you can least afford it.
Strictly, selling out costs you something extra as well: a guest who cannot have the dish sometimes picks something cheaper, sometimes nothing at all, and in the worst case comes back less willingly. That is real, but it cannot be quantified without guessing, and a guess inside a calculator looks exactly like a fact. So this model leaves it out — with the effect that the answer stays on the cautious side.
2. What one portion spare costs you
On the other side: you prepped one nobody ordered. What is that gone? Here too the first answer is usually wrong, and this time too high. It is not the menu price — you were never getting that — and it is usually not the full purchase price either.
Because a leftover portion is rarely worth nothing. It goes into the staff meal, it becomes tomorrow's soup, it moves to the lunch menu, it goes in the freezer where the component allows it, or it leaves through a surplus-food app at a third of the price. What you win back is called the salvage value, and it is the only number on this page you have complete control over.
On our special the plate costs €5.45 in ingredients and still returns about €1.35 as staff meal and soup. So one portion spare costs you €4.10. Beside the €12.61 above that is not even a third. That ratio — and not your feeling about waste — is what decides the rest of this page.
Watch one thing: salvage value is never equal to the purchase price, not even if you genuinely reuse everything. What you win back is the value of soup, not the value of a special, and there is always labour in between. The calculator below therefore caps salvage below the purchase price; set them equal and the model would advise you to prep infinitely.
Three dishes off the same menu show how far apart those two amounts can sit.
Same menu, same dining room, same trade. All that differs is what one portion short and one portion spare cost — and that moves the service level from just under sixty to almost a hundred per cent.
Fresh fish of the day€27.30 on the menu · €9.95 purchase · €0.00 salvage
Daily special€20.50 on the menu · €5.45 purchase · €1.35 salvage
Soup of the day€7.90 on the menu · €1.45 purchase · €1.15 salvage
The fresh fish is the dish you play tight on: expensive to buy, nothing recoverable, so a portion spare genuinely hurts — hence 59%. The soup is the opposite, 95%: cheap, and whatever is left simply carries on tomorrow, so you should almost never let it sell out. In most kitchens the exact opposite happens: the soup is gone by nine and three portions of fish are waiting.
3. The ratio between them is not a quantity — it is a percentage
This is where the whole argument turns. You now have two amounts: what one short costs and what one spare costs. Divide the first by the sum of the two and you get no number of portions but a percentage: €12.61 divided by €16.71 is 75%.
That percentage is your service level — the share of services on which you want enough standing ready. It says: on this dish, at this margin and this salvage value, it is worth not selling out on a good three services in four. On the remaining 25% you sell out deliberately, because it is cheaper to say no occasionally than to prep every service for those last few guests.
And here is the neatest part of the arithmetic: aim at exactly that percentage and the chance you do not sell out that service is exactly the same 75%. The percentage is the answer. The number of portions is only what that percentage costs in your kitchen.
Put it next to the average and the comparison hurts: prepping to the average is aiming at a 50% service level. Nobody would knowingly choose that for a dish that costs €12.61 per missed portion. Everybody does it.
The same twenty services, twice. The dashed line is what was prepped; every column is what was asked for.
Prepped to the average24 portions prepped
sold out on 10 of 20 services58 portions left58 portions missed
Prepped to your service level28 portions prepped
sold out on 6 of 20 services104 portions left24 portions missed
Prepping 4 portions more takes the number of services on which you have to say no from 10 to 6, and more than halves the portions you miss out on: from 58 to 24 over twenty services. It costs you 46 extra portions that do not leave the service — and that is exactly the trade the two amounts above are about.
4. The spread: from percentage to portions
A service level of 75% still says nothing about how much to cut. For that you need to know how hard your trade swings. On a dish that goes between 23 and 25 times every service, 75% is nearly the same number as the average. On one that goes between 13 and 36 times, it lands far above it.
You need no statistics for this. Two figures are enough: how many go on an ordinary service, and how many on a genuinely busy one — not your record, but a good Saturday. On our special that is 24 and 36. The distance between them is your room for error, and the calculator turns it, together with your percentage, into one number.
For this dish that comes out at 28, against the 24 standing there now. 4 portions more. You sell out on 25% of your services instead of 50%, you bin 4.9 portions per service on average instead of 2.4, and you earn €8 per service more on balance. Across 300 services a year that is about €2,535 — on one dish.
Do not know those two figures? Count them. Note after every service, for a fortnight, how many of this dish went and whether you sold out, and you have both. That is the same discipline as setting a fixed par level, and it is exactly the measurement the covers forecast already makes for your dining room.
Put your own dish into the calculator
Enter what the dish costs on your menu, what the ingredients cost, what a surplus still returns, and how many you sell on an ordinary and on a busy service. The fields are prefilled with the special from this guide — overwrite them with yours.
You get your two amounts, the service level that follows from them, the number of portions that goes with it, and what the difference from your current number is worth per year.
Portion calculation
Seven figures about one dish, and the number that has to be ready tomorrow.
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The model assumes your trade swings roughly symmetrically around your average and that a surplus returns the salvage value you enter. It does not count the goodwill of a guest who is told no, so the advice stays on the cautious side. Everything computes in your browser; nothing is sent or stored.
Two things to know when reading it. The number that comes out is an optimum across many services, not a forecast for tomorrow. On any individual service it will be too much or too little; that is not an error in the arithmetic, that is precisely what a service level of 76% means.
And it is a starting point per dish, not a kitchen policy. Run it once for your three best sellers and you will see they do not land on the same answer — which immediately explains why one rule of thumb for your whole mise en place never worked.
Three levers that change the answer without touching your forecast
Up to here everything was about choosing a number given the circumstances. But three of those circumstances you can move yourself, and then the answer changes shape. They are in order of what they return.
Give your surplus a route
Salvage value is the only input that is entirely yours. If a leftover portion goes in the bin today, then every portion spare costs you the full purchase price. If there is a standing destination ready — staff meal, tomorrow's soup, the lunch formula, a surplus app — it costs you a fraction of that.
On our special: raise salvage from €1.35 to €3.15 and your service level rises from 75% to 85%, and the dish returns €10 more per service. But watch what then happens to the quantity — it goes up, from 28 to 30, and your surplus from 4.9 to 6.5 portions. A route for your surplus makes waste cheaper, not smaller. That is a gain, but it is not the gain you were hoping for.
Cut your prep in two
This is the only lever that brings your sell-outs and your waste down at the same time, and therefore the most important of the three. The idea: do not prep everything before service, but set a base ready and hold the last step until during service. Portion and finish to order instead of finishing early, the sauce ready but the garnish only on the ticket, the second tray cut only once the first is half empty.
What you win there is not time but information. You decide on that last piece only once you already know how the evening is going, and therefore against a much smaller spread. Halve the room between an ordinary and a busy service — from 24–36 to 24–30 — and the advice drops from 28 to 26 portions, while your surplus goes from 4.9 to 2.5 per service and your chance of selling out stays exactly the same. That is almost half the waste at the same sales, and it is worth another €16 per service.
Not every dish splits, and where it does it costs more hands during service than before it. But it is the only move on this page where nobody loses, and it is why a well-built mise en place is worth more than a better forecast.
Let one ingredient carry three dishes
A component that sits in only one dish carries the full uncertainty of that one dish. That same component across three dishes carries the uncertainty of the sum, and that swings proportionally far less — three dishes rarely all have a bad evening at once.
In practice that means: the same confit onion on the burger, in the quiche and beside the sharing board; the same stock as the base for two soups and a risotto. You then no longer prep per dish but per component, against a spread that is smaller than the sum of the separate spreads. And what is left of that component is by definition not waste but stock, which pushes the salvage value from the first lever up by itself.
It is also the cheapest way to cut food waste without disappointing a single guest, and it explains why a short menu with a lot of cross-use structurally bins less than a long one with the same number of covers.
What you do with this week, this month and this quarter
Nobody manages everything at once, and there is no need: running one dish through the arithmetic already delivers nearly everything there is to get from this.
This week — run one dish through it
- Pick your best-selling dish with a short shelf life: the special, the fish, the soup.
- Look up your purchase price per portion in your recipe costing, and your VAT rate on your till receipt.
- Estimate honestly what one leftover portion still returns today. Zero is a valid answer, and usually an instructive one.
- Put it into the calculator above and compare the number with what was standing there this morning.
This month — measure instead of estimating
- Note two things after every service for that one dish: how many went, and whether you sold out.
- After a fortnight you have your ordinary service and your busy service, and the last two fields are no longer an estimate.
- Look at how often you sold out: if it is around half, you were prepping exactly to the average.
- Repeat the calculation for your three biggest dishes and put the numbers on your mise en place list.
This quarter — change the circumstances, not only the number
- Give every short-shelf-life dish one standing destination for its surplus, and write them on the card in the kitchen.
- Find, per dish, the last step you can move into service itself, and test it for a week.
- At your next menu change, let at least one component carry three dishes instead of one.
- Revisit the price of your daily special only after that: a higher margin raises your service level, but it solves no prep problem at all.
The right number feels too high, and it should
Almost every cook who runs this arrives at a number higher than what is standing there now, and the first reaction is that it must be wrong. It is not: one portion short costs most kitchens three to four times as much as one portion spare, and while that holds, being careful is the most expensive choice on the menu.
But the conclusion of this page is not "bin more". Raising the quantity is the gain you can take today; the real gain is in the second lever. Cut your prep in two and you decide on the last portions only once the evening is half gone — and that takes you from 4.9 to 2.5 portions of surplus per service without disappointing a single guest. That is the only answer on this page where nobody loses.
Then do the same with the rest of your purchasing. The number of portions you prep is the daily version of the same question your par levels answer, and together they decide how much of what you buy leaves as revenue instead of as waste.