Compare products by total contribution, contribution per constrained hour and contribution per pound of working cash to find what really earns most.
Short answer: Calculate each product's realised selling price minus every cost that changes when you sell one more unit. Then rank products three ways: total contribution over the period, contribution per hour of your constrained capacity, and contribution per pound of working cash required. Favour the product that wins on your current constraint and has enough proven demand, not automatically the one with the highest price or unit margin.
“Most profitable” can mean at least three different things. One product may produce the largest pounds per unit, another may contribute most across the month because it sells in volume, and a third may earn cash fastest from the machine time or stock budget you cannot expand.
My view is that allocating every fixed overhead across products is usually the wrong first ranking method for a small business. It makes shared rent, founder pay and administration look product-specific. Use contribution to choose what to make and sell next, then check that the whole product portfolio covers fixed costs and owner reward.
Use the Three-Yield Product Ranking
The Three-Yield Product Ranking compares each product through three economic yields. Each answers a different decision.
- Total contribution: Calculation: Unit contribution × units sold; Decision it answers: Which product added most towards fixed costs and profit in the period?; Main limitation: Rewards existing volume, even when demand was accidental
- Capacity yield: Calculation: Unit contribution ÷ constrained time per unit; Decision it answers: What should you prioritise when labour or equipment time is scarce?; Main limitation: Needs accurate time for the actual bottleneck
- Cash yield: Calculation: Unit contribution ÷ variable cash required per unit; Decision it answers: What uses a limited stock or production budget best?; Main limitation: Ignores how long cash remains tied up unless you add cycle time
Do not average the three rankings into a decorative score. Name your current constraint, use the corresponding yield first, and treat the other two as checks. If workshop hours are fully booked, capacity yield matters. If you have spare time but cannot fund materials, cash yield matters. If neither is constrained, total contribution and demand become more useful.
Calculate a defensible realised price
Start with what you actually retain per unit, excluding VAT where applicable and after discounts, refunds, sales commissions and channel deductions. A £60 listed product sold mainly through a marketplace with promotions may not have a £60 realised price.
Use a consistent period and divide net sales value by units kept by customers. Keep returns visible. If you sold 100 units for £5,500 after discounts but refunded 10 units for £550, the realised price across the 90 retained units is £4,950 ÷ 90 = £55. Ignoring returns would exaggerate both price and demand.
Compare like with like. Wholesale and direct retail may be separate product-channel combinations because the selling price, packing, commission and order handling differ. One physical item can therefore have two contribution calculations.
Include every genuinely variable cost
Variable cost is cash or economic cost that changes because you make and sell another unit. It commonly includes materials, product packaging, piece-rate labour, transaction charges, marketplace commission, outbound delivery that you pay, expected returns and consumables.
Founder time requires judgement. If another unit consumes time you could use for paid work or additional production, include that time in the capacity calculation even when you do not draw a wage for it. Calling your own time free makes labour-heavy products appear attractive and can build a business that cannot later hire at its current prices.
Do not force fixed rent or general bookkeeping into each unit unless the cost genuinely changes with the product decision. You should still test whether combined contribution covers those fixed costs. The distinction is about choosing the right product, not pretending overhead does not exist.
The core arithmetic is: unit contribution = realised price - variable cost per unit contribution margin percentage = unit contribution ÷ realised price × 100
Use pounds of contribution for resource decisions. A high percentage on a very small selling price can still produce less money per scarce hour than a lower-percentage premium product.
Find the real constraint
Ask what prevents you from selling one more unit this month. The answer must be specific: 40 laser-cutting hours, £3,000 of material cash, 12 metres of display space, or the number of qualified customer enquiries. “Time” is too broad if only one production stage is full.
Measure each product's use of that constraint. Include setup time by sensible batch size. If a machine takes 30 minutes to set up and then five minutes per unit for a batch of ten, constrained time is eight minutes per unit, not five.
When demand is the constraint, resource yield alone cannot create sales. Rank contribution from realistically obtainable volume, then test a focused change in placement, offer or sales effort. Do not discontinue a product solely because its theoretical hourly yield is weak when it draws customers who later buy a stronger product. That relationship needs evidence from actual baskets or enquiries.
Worked example: Tide & Timber Bird Feeders
Tide & Timber makes three wooden bird feeders. Workshop finishing time is fully used, and the owner also wants to protect a limited material budget. These illustrative figures use realised prices after normal discounts and variable costs including wood, fittings, packaging and payment charges.
- Window feeder: Realised price: £55; Variable cost: £19; Unit contrib ution: £36; Finishing time: 0.6 hours; Monthly units: 65; Total contri bution: £2,340; Contributio n per hour: £60.00; Contributio n per £1 variable cash: £1.89
- Hanging feeder: Realised price: £85; Variable cost: £38; Unit contrib ution: £47; Finishing time: 1.5 hours; Monthly units: 40; Total contri bution: £1,880; Contributio n per hour: £31.33; Contributio n per £1 variable cash: £1.24
- Feeding station: Realised price: £180; Variable cost: £105; Unit contrib ution: £75; Finishing time: 3.0 hours; Monthly units: 12; Total contri bution: £900; Contributio n per hour: £25.00; Contributio n per £1 variable cash: £0.71
The feeding station has the highest unit contribution at £180 - £105 = £75. If the owner looked only at pounds per sale, it would appear to be the winner.
The window feeder contributes most in total: £36 × 65 = £2,340 a month. It also produces £36 ÷ 0.6 = £60 per constrained finishing hour, compared with £75 ÷ 3 = £25 for the station. Its cash yield is £36 ÷ £19 = £1.89 of contribution for every £1 of variable cash, against £75 ÷ £105 = £0.71 for the station.
With finishing time and working cash constrained, the lowest-priced item wins all relevant rankings. Shifting one three-hour production slot from a feeding station to five window feeders would change contribution from £75 to 5 × £36 = £180, an increase of £105, provided those five feeders can be sold without extra discounting.
That condition matters. Tide & Timber should not make unlimited window feeders from a spreadsheet result. It should test demand for the next 20 units, watch realised price and returns, and then allocate the next batch. The arithmetic identifies where to test, not what the market is guaranteed to buy.
Add portfolio effects only when you can observe them
Some products earn less directly but help sell something else. A low-priced trial size may acquire customers, a spare part may support the main product, and a premium option may make the standard version easier to choose. These effects can be real.
Measure them rather than defending them by instinct. Compare baskets, repeat purchases, enquiries and cancellations. If 30% of customers who buy Product A later buy Product B, calculate the added contribution using your own records and a suitable time window. If you cannot trace the effect, keep the claim separate from the base product ranking.
Also distinguish strategic learning from permanent subsidy. A new product may deserve a defined trial even with weak initial yield, but give the trial a unit limit, decision date and pass condition. “It builds the brand” is not a sufficient reason to carry an indefinite loss.
Related guides
What to do over the next seven days
Today, choose your latest normal trading period and calculate realised price, variable cost and unit contribution for every material product-channel combination. Reconcile total units and sales value to your records. Do not allocate shared overhead yet.
Tomorrow, name the one resource limiting additional contribution and measure each product's use of it. Complete the Three-Yield Product Ranking, then mark products to grow, repair, retain deliberately or pause.
For the next five days, test the winner on a bounded batch or the next 20 suitable enquiries. Track realised price, variable cost, constrained time and units sold. At the end of day seven, compare actual added contribution with the displaced alternative, then set the following production or sales allocation.
Frequently asked questions
Is gross margin the same as product profit?
No. Gross margin usually subtracts direct cost of sales from revenue, but definitions vary between businesses and accounting systems. Product contribution goes further when it subtracts every cost that changes with an additional sale, such as transaction fees, outbound delivery or expected returns.
Neither figure automatically includes shared rent, administration or owner reward. Define the calculation beside your report so comparisons stay consistent. Use contribution for the next-unit and constrained-resource decision, then compare total contribution across the portfolio with fixed operating costs to judge whether the business as a whole makes enough money.
Should I include my own labour in the product cost?
Yes, account for your time whenever making another unit consumes capacity that has an alternative use. Record minutes by production stage and use contribution per constrained hour, even if you do not yet pay yourself an hourly wage. You can also include a replacement labour cost in scenario testing to see whether the product survives hiring.
Do not add the same labour twice as both a variable cost and constrained resource without understanding the calculation. If your time is currently spare and demand is scarce, cash contribution may guide the immediate sale, but a price that only works with permanently unpaid labour is not sustainable.
What if my highest-contribution product sells very slowly?
Rank it using realistic obtainable volume, not theoretical production. A £100 unit contribution creates only £500 if five units sell, while a £20 contribution creates £2,000 if 100 units sell. Keep demand evidence alongside the Three-Yield Product Ranking. You can test whether placement, targeting or price presentation improves sales, but cap the test by time and stock cash.
If slow turnover ties up scarce cash for months, add a time measure such as contribution per £1 of cash per month. A product is economically attractive only when customers buy it within the period your business can support.
How should I handle products that share materials?
Assign the material actually consumed by each unit at its current replacement cost, including normal waste. If buying a shared material in larger quantities changes the price, compare the next relevant order rather than spreading an old bulk discount forever.
When material itself is scarce, calculate contribution per scarce unit, such as contribution per metre of fabric, alongside the three standard yields. Joint production can require a different treatment when one process inevitably creates multiple outputs. In that case, avoid arbitrary allocations for short-term decisions and ask your accountant to help design a consistent reporting method.
Should I discontinue every product below the average margin?
No. An average guarantees that some products sit below it, and removing them can make the remaining average worse if they still contribute towards fixed costs. Compare each product with the best realistic use of the resource it consumes.
Keep a weaker product when it adds positive contribution without displacing a stronger sale, supports a measured portfolio role or serves an important contractual need. Pause it when it consumes constrained time or cash that would earn more elsewhere and no repair is credible. Check customer and channel effects before acting, then test the change on a bounded period.
How do returns and discounts affect the ranking?
Use realised results, not list prices. Subtract discounts and refunds from sales value, divide by units retained by customers, and include the expected variable cost of returns, replacement shipping and damaged stock where your records support it. Compare products over the same period so a promotional week does not distort one line unfairly.
If returns are volatile, show the base result and a higher-return case rather than hiding uncertainty inside an unsupported average. A product with a strong list-price margin can fall sharply once frequent discounting and return handling are included, which is precisely why realised price matters.
How often should I recalculate product profitability?
Review it monthly while costs, prices or product mix are changing, and immediately after a material supplier increase, channel fee change or repeated return problem. A stable business may move to a quarterly deep review while monitoring unit contribution exceptions each month.
Use replacement costs for forward decisions, because last year's cheap stock will not fund the next purchase. Preserve the prior calculation so you can distinguish a real economic shift from a data correction. Do not change production priorities for tiny weekly movements. Recalculate when new evidence could alter which product wins on your current constraint.
Comments (0)