IB Economics Profit Revenue & Costs

Show Me the Money: Revenue, Costs, and Making a Profit

"What is the profit maximising condition in economics?"

The Lemonade Stand That Nearly Went Bust

Let's go back to your childhood and say you decide to set up a lemonade stand this summer. You're feeling entrepreneurial, you've watched one too many episodes of Dragon's Den, and you reckon you got what it takes. Fresh lemons, a folding table, a hand-written sign. You charge £1 per cup, and on your first Saturday you sell 80 cups. Happy days.

Except...you realise you have spent £30 on lemons. £10 on sugar. The table cost you £20 to rent from a mate. And you paid your little sister £15 to help out. That's £75 in costs. You made £80 in sales. Your profit? A grand total of… £5.

Was it worth it? Probably not. But without intending to you've just stumbled headfirst into one of the most important relationships in all of economics - the one between revenue and costs.

And once you understand this relationship properly, you'll understand how every business on this planet at least - from your lemonade stand to Apple's $416 billion empire - makes decisions about what to produce and how much to charge.

Total Revenue: The Headline Number

Total revenue (TR) is the total income a firm receives from selling its output. It is calculated using the formula TR = P × Q, where P is the price per unit and Q is the quantity sold.

The formula is incredibly simple:

TR = P × Q (Price × Quantity sold)

Your lemonade stand: £1 × 80 cups = £80 TR. Simple.

Now scale that up. Apple's total revenue for fiscal year 2025 hit a record high of $416 billion, with iPhone generating around 50% of that revenue and the Services segment - think App Store, Apple Music, iCloud - contributing roughly about 26%.

That's P × Q working on a genuinely massive scale.

Microsoft, meanwhile, reported $252 billion in total revenue for FY2025, with its Intelligent Cloud segment - dominated by Azure - reaching $100.4 billion. Azure alone grew by 34% year-on-year, which tells you everything about where the money is flowing in the tech world right now.

Two firms. Two very different products. The same formula: P × Q.

Total Costs: Get It Wrong And It Will Hurt You

Revenue is the exciting number. Costs are the ugly one.

Costs are all the expenditures involved in the production process - everything a firm spends to make and sell its product. And they come in two different types:

Fixed Costs

Fixed costs are production costs that remain constant regardless of how much output a firm produces. Examples include rent, loan repayments, and management salaries. Fixed costs must be paid whether a firm produces zero units or ten thousand.

Quick IB Economics examples: rent on a factory. The salary of your IT manager. The monthly repayments on a bank loan. They don't care how busy or successful you are - they land in your inbox every single month regardless.

For your lemonade stand, the table rental (£20) is a fixed cost. You paid it whether you sold 1 cup or 100.

Variable Costs

Variable costs are production costs that change in direct proportion to a firm's level of output. As a firm produces more, variable costs rise; as output falls, they fall. Raw materials and piece-rate wages are typical examples.

Lemons and sugar are classic variable costs for your stand. The more lemonade you make, the more you spend on ingredients. For you slightly annoying when lemon prices spike in January.

For a major manufacturer like Toyota, variable costs include the steel, rubber, and electronics that go into each car. Build more cars, spend more on materials.

Total Cost: The Full Picture

Put them together and you get:

Total cost (TC) is the sum of all production costs incurred by a firm. It is calculated as TC = TFC + TVC, where TFC is total fixed costs and TVC is total variable costs.

Your lemonade stand: £20 (table rental, fixed) + £55 (lemons, sugar, sister's wages, variable) = £75 TC

Apple's total cost of goods and services in FY2025? Considerably more than £75. But the maths is identical. The basic formula always works.

Marginal Revenue and Marginal Cost: A Smart Way to Think About Production

So far we've been looking at total figures. But businesses don't just ask "how much did we make this year?" They ask: "Should we produce one more unit? Is it worth it?"

That's where marginal thinking comes in.

Marginal Revenue (MR)

Marginal revenue (MR) is the additional revenue a firm earns from selling one extra unit of output. It is calculated as MR = ΔTR ÷ ΔQ (the change in total revenue divided by the change in quantity sold).

Imagine your lemonade stand sells 80 cups at £1 each (TR = £80). Then a thirsty cyclist turns up and buys cup number 81. Your TR jumps to £81. The marginal revenue of that extra cup? £1.

Marginal Cost (MC)

Marginal cost (MC) is the additional cost incurred by producing one extra unit of output. It is calculated as MC = ΔTC ÷ ΔQ (the change in total costs divided by the change in quantity produced). Marginal cost typically falls initially due to economies of scale before rising as diminishing returns set in.

To make that 81st cup of lemonade, you had to squeeze another lemon and use a bit more sugar. Let's say that cost 40p. Your MC is £0.40.

Should you make it? Absolutely - you receive £1 but it only costs you 40p to produce. You're 60p better off. Keep going.

The Key Point: Where MC Meets MR

Now here's a key idea for you - the one that unlocks the logic of every profit-maximising firm on Earth.

The profit maximising condition states that a rational firm maximises profit by producing at the output level where marginal cost (MC) equals marginal revenue (MR). When MR exceeds MC, producing an additional unit adds more to revenue than to cost, so profit rises. When MC exceeds MR, the additional unit costs more to produce than it earns, so profit falls. Profit is therefore maximised at the point where MC = MR.

Let's understand why:

• When MR > MC: selling an extra unit brings in more revenue than it costs to produce. Your firm is leaving money on the table. Produce more.

• When MC > MR: that extra unit costs more to produce than you earn from selling it. You're actively losing money on it. Produce less.

• When MC = MR: you've hit the sweet spot. One more unit would cost more than it earns. One fewer unit would sacrifice profit. This is your profit-maximising output level.

Not too much, not too little - just the right amount of production.

• Internal Assessment (IA) Guide – Free Download
  Step-by-step support on topic selection, structure, evaluation, and most common IB Economics IA mistakes.

• Understanding key IB Economics Internal Assessment concepts

• Applying and explaining them in real-world IB Economics contexts

• Building IB Economics IA confidence without drowning in dry theory and explanations.

Download the IA guide now for free and boost your IB Economics grades and confidence

Abnormal Profit: When Things Go Very, Very Well

Right, so firms aim to maximise profit. But what does maximum profit actually look like? This is where economists introduce some precise terminology that'll serve you brilliantly in exams.

Abnormal profit (also called supernormal profit or economic profit) is the profit earned by a firm above and beyond normal profit. It occurs when average revenue (AR) exceeds average cost (AC), meaning the price received per unit is greater than the cost per unit. Abnormal profit signals to new firms that a market is attractive to enter, driving competition and eroding those profits over time - at least in competitive markets:

Abnormal profit occurs when AR > AC (Average Revenue > Average Cost)

In other words, the price received per unit is higher than the cost per unit. The firm is doing better than just keeping the lights on and opening its doors - it's genuinely thriving.

Economists consider implicit costs (also called opportunity costs) when calculating profit. Abnormal profit means earnings that exceed the required return on the firm's investment - including what they could have earned by doing something else with their money.

IB Economics Real-life examples? Look no further than Big Tech. Apple's total revenue for FY2025 hit a record high of $416 billion, and its Services segment alone hit an all-time quarterly record - up over 15% year-on-year - showing everyone how successful is their competitive ecosystem. Apple's brand loyalty and control over its ecosystem allows it to charge prices well above average cost. That gap between AR and AC? That's abnormal profit - in outstanding fashion.

The signal that abnormal profit sends to the market is crucial: it sends a clear message "get in here, there's money to be made." New firms are attracted into the industry, competition intensifies, and over time - at least in theory - those supernormal profits get competed away. (In practice, Apple's barriers to entry are formidable enough that rivals haven't exactly touched their margins.)

Normal Profit: Not as Boring as It Sounds

You might think "normal profit" means "nothing exciting is happening." But economists have a very specific - and actually quite profound - definition.

Normal profit (also called zero economic profit) is the minimum level of profit a firm needs to justify remaining in its current business activity. It covers all explicit costs and all implicit costs, including the opportunity cost of the entrepreneur's time and capital. Normal profit occurs when AR = AC. Crucially, normal profit does not mean zero accounting profit - it means the firm is earning exactly what it could have earned in its next best alternative use of resources.

The condition for normal profit is AR = AC

When average revenue exactly equals average cost, the firm is breaking even in the economic sense. It's not earning extra - but crucially, it's earning enough. The owner is getting paid what they could have earned elsewhere. There's no reason to leave, but equally no massive incentive to stay beyond what they're already getting.

My students often have issues understanding the following concept so pay attention: zero economic profit does NOT mean no profit. It means no abnormal profit. The firm is still generating revenue, covering all its costs (including a reasonable return for the owner), and continuing to operate. Economists treat normal profit as a cost of production - because without it, there's no incentive to run the business at all.

IB Economics Real-life examples? Think of a small independent bakery on your high street. It covers its rent, its flour and butter costs, the baker's wages, and gives the owner a decent enough income that they don't pack it in and retrain as an accountant. That's normal profit. Not glamorous - but a viable feasible business.

Losses: When It All Goes Wrong

And then there's the other side of the coin.

A loss occurs when a firm's total costs exceed its total revenue (TC > TR), or equivalently when average cost exceeds average revenue (AC > AR). In the short run, a loss-making firm may continue operating if it covers its variable costs and makes some contribution toward fixed costs. In the long run, a firm must earn at least normal profit to remain viable.

TC > TR - or in per-unit terms - AC > AR

The price being charged isn't enough to cover the unit costs of production. The firm is essentially subsidising every sale it makes from its own reserves. Not sustainable.

A loss-making firm can continue operating in the short run - particularly if it's covering its variable costs and making some contribution toward fixed costs. In the short run, fixed costs are already committed and can't be recovered, so carrying on might still make sense even if losses are being made overall.

But in the long run, a business must generate at least normal profit - enough to pay its suppliers, employees, and financiers. A firm that persistently fails to achieve this will eventually close down and exit the market.

IB Economics Real-life examples? Think of the wave of restaurant and retail closures that swept the UK during the post-pandemic cost-of-living squeeze. Energy bills (fixed costs) rocketed. Raw material costs (variable costs) surged. But many firms couldn't pass these costs on to increasingly cautious consumers without losing their customer base entirely. The result? TC > TR. Losses. Closures.

For access to all IB Economics exam practice questions, model answers, IB Economics complete diagrams together with full explanations, and detailed assessment criteria, explore the Complete IB Economics Course

IB Economics Summary

Here's the cleanest summary of the whole lesson:

Rational producers maximise profit by producing at the output level where MC = MR - the point at which squeezing out one more unit stops being worth it.

IB Economics Exam Tip

When writing about profit maximisation, don't just state that "firms produce where MC = MR." Explain the logic in both directions - what happens if the firm produces more than this (MC > MR, so losses on the marginal unit) and what happens if it produces less (MR > MC, so money is being left behind). Walking the examiner through both sides demonstrates genuine understanding and will earn you the marks you are working hard for.

Also, watch out for the normal profit trap: never write that normal profit means "no profit." It means no abnormal profit. That distinction comes up surprisingly often in IB Economics exam mark schemes.

Frequently Asked Questions

What is the formula for total revenue in economics? Total revenue (TR) is calculated using the formula TR = P × Q, where P is the price charged per unit and Q is the quantity of units sold. If a firm sells 500 units at £10 each, its total revenue is £5,000.

What is the difference between fixed costs and variable costs? Fixed costs remain constant regardless of how much a firm produces - rent and loan repayments are classic examples. Variable costs change with the level of output - raw materials and wages paid per unit produced rise and fall with production. Total cost is the sum of both: TC = TFC + TVC.

Why do firms produce where MC equals MR? Producing at the point where marginal cost (MC) equals marginal revenue (MR) maximises profit. If MR is greater than MC, producing one more unit adds more to revenue than to cost, so profit rises. If MC is greater than MR, the last unit costs more to make than it earns, reducing profit. The firm should therefore neither produce more nor less than the MC = MR output level.

What is the difference between normal profit and abnormal profit? Normal profit is the minimum return needed to keep a firm operating in its current activity - it covers all costs including opportunity costs, and occurs when AR = AC. Abnormal profit (also called supernormal or economic profit) is anything earned above that level, occurring when AR > AC. Normal profit does not mean no profit - it means no extra profit beyond what the entrepreneur could have earned elsewhere.

Can a firm survive while making a loss? In the short run, yes - as long as a firm's revenue covers its variable costs, it makes sense to keep operating rather than shut down immediately, since fixed costs must be paid regardless. In the long run, however, a firm must earn at least normal profit to remain viable, cover all its obligations, and justify continuing in business.

Every episode of Pint-Sized links back to what matters most for your IB Economics course:

• Understanding key IB Economics concepts

• Applying them in real-world IB Economics contexts

• Building IB Economics course confidence without drowning in dry theory.

Subscribe for free to exclusive episodes designed to boost your IB Economics grades and confidence

IB Economics Diagrams Programme, What's included:

• 200+ exam-ready diagrams covering the entire IB Economics syllabus

• Video for every diagram showing you exactly how each model looks

• Image version perfect for modelling diagrams in you essays, presentations, and your IA

• Detailed written explanations of the IB Economics theory behind each diagram

• Both SL and HL IB Economics diagrams clearly labelled and organised by topic

• Real IB Economics exam application showing how to use diagrams effectively in Paper 1 and Paper 2

Next Up: Monopoly

In Part 3, we dive into monopolies - where one firm calls the shots, controls supply, and sets prices like the market’s master. Get ready for some serious economic stories.

Stay well,

Related Topics:

IB Economics Hub Page

IB Economics Module 2 Microeconomics Hub Page

IB Economics Diagrams Page for all market power diagrams

IB Economics Market Power Hub Page

IB Economics Monopoly Hub Page

What is Perfect Competition? normal profit in the long run is a direct consequence of free entry in perfect competition;

Market Failure Hub Page abnormal profit tied to monopoly power has a direct relationship with allocative inefficiency and market failure

IB Economics Paper 3 HL Guide - MR = MC profit maximisation appears heavily in quantitative Paper 3 questions

Read Next: IB Economics Monopoly and Natural Monopoly