Marginal cost
Learn what marginal cost is, how to calculate it and how to use it to price and plan production with confidence.
Published Wednesday 30 September 2026
Table of contents
Key takeaways
- Marginal cost is the extra cost of producing one more unit, and it comes from variable costs such as materials and direct labour
- You calculate it by dividing the change in total cost by the change in quantity produced
- Each extra unit adds to your profit while its marginal cost stays below the price you sell it for
- Marginal costing guides everyday pricing and order decisions, while financial statements value inventory using absorption costing
What is marginal cost?
Marginal cost is the extra cost you take on when you produce one more unit of a product or serve one more customer. It tells you whether making more will add to your profit.
Say you run a candle business. Making 100 candles costs S$320 and making 101 costs S$325, so your marginal cost for the 101st candle is S$5.
That S$5 comes from costs tied directly to production, such as wax and wicks. These are variable costs, which rise and fall with your output. Fixed costs like rent stay the same when you make one more candle, so they don’t change your marginal cost.
You’ll often see marginal cost next to two other cost measures:
- Total cost is everything you spend to produce all your units, fixed and variable costs combined
- Average cost is your total cost divided by the number of units, a per-unit figure that blends fixed and variable costs
Marginal cost looks only at the next unit. That makes it the number to check when you’re deciding whether to produce more.
Why marginal cost matters for your business
Marginal cost gives you a hard number to test decisions against before you spend money. Pricing is usually where it pays off first.
Say an extra batch costs S$12 per unit and you sell at S$20. Each extra sale then adds S$8 towards your fixed costs and profit, so you can weigh up bulk discounts and wholesale deals with real figures.
These cost-based pricing strategies show more ways to set prices around what you spend.
The same number sharpens your planning. When you know what your next production target will cost, your budgets and cash flow estimates rest on real per-unit figures.
Tracking marginal cost month by month also shows you where production gets expensive. If your cost per extra unit climbs after 500 units a month, that’s the point to add equipment or hire help. A steady rise over three months is an early sign to check supplier prices and waste while there’s still time to act.
Marginal cost also helps you judge new opportunities quickly, because it shows whether extra work adds profit. When a customer asks for a large or custom order, compare the price on offer with your marginal cost. You’ll find more ways to lift your margins in this guide to growing your profits.
What’s included in marginal cost
Marginal cost includes only the costs that change when you make one more unit. For most small businesses, these costs go into the calculation:
- Direct materials, such as ingredients or fabric
- Direct labour paid by the hour or per piece, including overtime
- Variable production overheads, such as power for machines and packaging
- Per-order selling costs, such as delivery fees and sales commissions
Fixed costs stay out of the calculation because they don’t move with each extra unit. Rent, insurance, salaries and equipment leases fall into this group, along with most other business overheads.
Some costs sit in both camps. A delivery van’s lease is fixed, but its fuel rises with every extra trip, so only the fuel counts towards marginal cost.
Marginal cost formula
The marginal cost formula compares how much your total cost changes with how much your output changes. Here’s the formula:
Marginal cost = change in total cost ÷ change in quantity
Each part of the formula measures one thing:
- Change in total cost is your total cost at the new output level minus your total cost at the original level
- Change in quantity is the number of extra units you produce, which could be a single unit or a full batch
Because fixed costs stay the same, the change in total cost comes from variable costs. Dividing it by the change in quantity gives you the cost of each extra unit.
How to calculate marginal cost
You can calculate marginal cost in three steps. This example follows a business that raises its output by 50 units.
- Work out the change in total cost by subtracting your original total cost from your new total cost. If 200 units cost S$2,000 and 250 units cost S$2,400, the change is S$400.
- Work out the change in quantity by subtracting your original output from your new output. Here, 250 minus 200 gives you 50 extra units.
- Divide the change in total cost by the change in quantity. S$400 divided by 50 gives you a marginal cost of S$8 per unit.
Next, compare that figure with your selling price. If you charge S$15 per unit, each extra unit contributes S$7 towards your fixed costs and profit.
Marginal cost example
A worked example shows how marginal cost helps you decide on a new order. Picture a small bakery in Singapore that makes sourdough loaves.
Last month, the bakery made 300 loaves for a total cost of S$1,800. That’s S$900 in fixed costs, such as rent and equipment leases, plus S$900 in variable costs, such as flour and packaging.
This month, a local café asks for an extra 50 loaves each month. Baking 350 loaves brings total cost to S$1,980: fixed costs stay at S$900, while variable costs rise to S$1,080.
The change in total cost is S$1,980 minus S$1,800, or S$180. The change in quantity is 50 loaves. That gives a marginal cost of S$180 ÷ 50 = S$3.60 per loaf.
If you charge the café S$6.00 a loaf, each extra loaf earns you S$2.40, or S$120 a month across the order. You’ll find more worked scenarios in this guide to calculating marginal cost.
Your average cost at 350 loaves is S$1,980 ÷ 350 = S$5.66 per loaf, well above the S$3.60 marginal cost. Your S$900 in fixed costs is already covered, so the extra loaves only need to pay for their own ingredients and packaging.
The marginal cost curve
Plot marginal cost against output on a graph and you’ll usually see a U-shaped curve. Knowing where you sit on it helps you spot cost changes before they reach your bank account.
On the left of the curve, marginal cost falls as output rises. You buy materials in bigger quantities and your team gets quicker at each task.
The bottom of the U is your most efficient output level, where each extra unit costs the least. For a small business, this point usually matches the capacity of your current equipment and team.
On the right, marginal cost climbs again because of diminishing returns. Staff start working overtime, and suppliers may add rush fees for larger orders.
Aim to operate near the bottom of the curve. If your cost per extra unit keeps rising, you’re on the upslope, and it may be time to add capacity.
Short-run vs long-run marginal cost
Adding capacity changes which costs count, so marginal cost depends on the time frame you look at. The difference comes down to which inputs you can change.
Here’s how the two time frames compare:
- Short-run marginal cost assumes some inputs are fixed, such as your premises and equipment, so it rises as you get close to full capacity
- Long-run marginal cost assumes every input can change, including the size of your premises and how many machines you run
For the bakery, the short run means working with one oven, so extra loaves eventually mean overtime. In the long run, you could add a second oven, which can lower the cost of each extra loaf once demand fills it.
Marginal cost vs marginal revenue
Marginal revenue is the extra income you earn from selling one more unit. Comparing it with marginal cost shows you the output level that makes the most profit.
If you sell at a fixed price, your marginal revenue equals that price. Charge S$20 per unit and each extra sale brings in S$20.
Use these checks when you compare the two:
- When marginal cost is below marginal revenue, each extra unit adds profit
- When marginal cost equals marginal revenue, you’ve reached the most profitable output at that price
- When marginal cost is above marginal revenue, each extra unit reduces profit, so scale back or review your price
- When a customer asks for a discount, accept the order if the discounted price still sits above your marginal cost
Marginal cost vs average cost
Marginal cost and average cost both measure production costs per unit, but they answer different questions. Average cost is your total cost divided by the number of units, so it blends fixed and variable costs.
The two numbers move in a set pattern. While marginal cost sits below average cost, each extra unit pulls your average down. Once marginal cost rises above average cost, each extra unit pushes the average up, so average cost is lowest where the two meet.
Average cost sets your pricing floor, because you need to sell above it to cover all your costs over time. Marginal cost tells you whether one more order or batch is worth taking on.
Marginal costing vs absorption costing
Marginal costing and absorption costing are two ways to value what you produce, and they treat fixed production overheads differently. The method you use changes the cost per unit you see in your reports.
Here’s how each method works:
- Marginal costing counts only variable costs as the cost of each unit and records fixed overheads as an expense in the period they occur
- Absorption costing adds a share of fixed production overheads to each unit, so part of them sits in inventory until the goods sell
Under International Accounting Standard 2 (IAS 2), inventory cost includes conversion costs such as production overheads, so financial statements use absorption costing. Marginal costing is the better fit for internal decisions like pricing and accepting orders, where you want to see each extra unit’s effect on profit.
Using marginal cost for contribution margin and break-even
Marginal cost is the starting point for two more useful numbers. Contribution margin shows how much each sale adds towards fixed costs, and the break-even point shows how many sales you need to cover them.
Two formulas do the work:
- Contribution per unit = selling price per unit minus marginal cost per unit
- Break-even units = total fixed costs ÷ contribution per unit
Go back to the bakery’s first month and assume every loaf sells for S$6.00. Each loaf costs S$3.00 in variable costs (S$900 ÷ 300 loaves), so contribution per loaf is S$3.00.
With S$900 in fixed costs, break-even is S$900 ÷ S$3.00 = 300 loaves. That matches the first month exactly: 300 loaves at S$6.00 brings in S$1,800, the same as total cost.
Every loaf above 300 adds to profit. The gap between your actual sales and break-even is your margin of safety. This guide to the margin of safety formula shows how to work it out.
Marginal cost vs stepped costs
Marginal cost assumes your costs rise smoothly as you produce more. In practice, some costs jump in steps once you pass a capacity limit.
Stepped costs, also called step-fixed costs, stay flat across a range of output and then jump when you cross a threshold. Warehouse rent is a good example: you pay the same whether you store 100 boxes or 900, but storing 1,000 means renting a second unit.
You’ll see stepped costs in situations like these:
- Hiring another employee when your team reaches its full workload
- Leasing a second machine when the first runs at full capacity
- Moving to larger premises when you fill your floor space
- Adding a delivery vehicle when your current van is fully booked
Marginal cost on its own won’t show these jumps. If each extra unit costs S$4 but unit 501 triggers a S$2,000 equipment lease, that 501st unit costs far more than S$4.
Map your stepped costs alongside your marginal costs so you know where each threshold sits. You can then time growth for when demand covers the higher cost, and build the cash outlay into your cash flow forecast.
Limitations of marginal cost
Marginal cost works best for short-term decisions about pricing and output. Keep these limits in mind when you use it:
- It leaves out fixed costs, so prices set at marginal cost alone won’t cover rent and salaries over time
- It assumes variable cost per unit stays constant, even though supplier prices and volume discounts can shift it
- It can hide stepped costs that jump once you pass a capacity threshold
- It can’t be used for external financial reporting, which calls for absorption costing
Track your costs with Xero
Marginal cost is only as reliable as the cost data behind it. Xero brings your transactions in through automated bank feeds, so your variable and fixed costs stay up to date.
You can run financial reports to compare costs month by month, then make pricing and production calls with confidence. Try Xero today and get one month free.
FAQs on marginal cost
Here are quick answers to more questions about marginal cost.
What causes marginal cost to increase?
Higher supplier prices and rising hourly wages push marginal cost up. If you import materials, a weaker Singapore dollar can raise it too.
Can marginal cost be negative?
It can in rare cases, such as when a bigger order unlocks a supplier discount that applies to every unit you buy. Your total cost then drops even though you’re producing more.
How does marginal cost relate to supply and demand?
In economics, the rising part of the marginal cost curve shapes how much a business will supply at each price. When demand pushes prices up, extra units become worth producing even at a higher marginal cost.
How does marginal cost apply to service businesses?
For a service business, marginal cost is what one more client or job costs you, such as contractor hours and software licences. Your own time counts too, so value it at what you’d pay someone else to do the work.
When should you calculate marginal cost?
Calculate it before you quote a large order or change your prices. A quarterly check also helps you spot supplier price changes early.
Related terms
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Disclaimer
This glossary is for small business owners. The definitions are written with their requirements in mind. More detailed definitions can be found in accounting textbooks or from an accounting professional. Xero does not provide accounting, tax, business or legal advice.