Having a reliable IGCSE formula sheet is essential for effective revision. While subjects like Physics and Chemistry have well-known formula lists, students often overlook the important formulas and key equations in IGCSE Biology and IGCSE Economics. This quick reference guide compiles every formula, equation, and quantitative concept you need for both subjects — perfect for last-minute revision and ongoing study.

IGCSE Biology Formula Sheet

Biology may seem like a content-heavy subject with less mathematical focus, but there are several essential formulas and calculations that appear regularly in IGCSE Biology exams. Mastering these will help you pick up marks that many students miss.

Magnification Formula

One of the most frequently tested calculations in IGCSE Biology:

Magnification = Image Size ÷ Actual Size

This can be rearranged to find any of the three values:

• Image Size = Magnification × Actual Size
• Actual Size = Image Size ÷ Magnification

Key tips:

• Always convert units to the same measurement (usually micrometres, μm) before calculating
• 1 mm = 1000 μm
• Show your unit conversions clearly in exam answers
• This formula appears in almost every Biology Paper 2/3

Percentage Change Formula

Used frequently in osmosis experiments and growth studies:

Percentage Change = (Final Value − Initial Value) ÷ Initial Value × 100

Common applications:

• Change in mass during osmosis experiments
• Population growth rates
• Changes in pulse rate during exercise experiments

Exam tip: Always include the positive or negative sign — a negative percentage change indicates a decrease.

Rate of Reaction/Process

Used in enzyme experiments, photosynthesis investigations, and respiration studies:

Rate = 1 ÷ Time

Or for measuring volume:

Rate = Volume of Gas Produced ÷ Time

Applications:

• Rate of enzyme activity at different temperatures
• Rate of photosynthesis (measured by oxygen bubble count or volume)
• Rate of respiration (measured by CO₂ production)

Photosynthesis Equation

The word equation and balanced chemical equation that every IGCSE Biology student must know:

Word equation: Carbon dioxide + Water → Glucose + Oxygen (in the presence of light energy and chlorophyll)

Balanced equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Aerobic Respiration Equation

Word equation: Glucose + Oxygen → Carbon dioxide + Water + Energy

Balanced equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)

Anaerobic Respiration Equations

In animals (and humans): Glucose → Lactic acid + Energy

In yeast (fermentation): Glucose → Ethanol + Carbon dioxide + Energy C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + Energy

Body Mass Index (BMI)

Sometimes tested in the health and disease section:

BMI = Body Mass (kg) ÷ Height² (m²)

Categories:

• Below 18.5: Underweight
• 18.5–24.9: Normal
• 25.0–29.9: Overweight
• 30.0 and above: Obese

Genetic Cross Ratios

While not a formula per se, you must be able to calculate and express:

• Monohybrid cross ratios: 3:1 (heterozygous × heterozygous) or 1:1 (heterozygous × homozygous recessive)
• Probability of offspring genotypes: Express as fractions, percentages, or ratios
• Example: If both parents are Bb, probability of bb offspring = 1/4 = 25%

Sampling and Estimation

Used in ecology fieldwork questions:

Estimated Population Size = (Number in First Sample × Number in Second Sample) ÷ Number of Recaptured Marked Individuals

This is the Lincoln Index (capture-recapture method), frequently tested in Paper 5/6 (practical).

Percentage of Cells in a Stage of Mitosis

Percentage = (Number of Cells in Stage ÷ Total Number of Cells) × 100

Used when counting cells in microscope images or root tip squash preparations.

Simpson’s Diversity Index

Sometimes tested at the Extended level:

D = 1 − Σ(n/N)²

Where:

• D = diversity index
• n = number of individuals of each species
• N = total number of all individuals

Biology Formula Quick Reference Table

Formula	Equation	Common Use
Magnification	M = I ÷ A	Microscopy calculations
Percentage change	(Final − Initial) ÷ Initial × 100	Osmosis, growth
Rate	1 ÷ Time	Enzyme experiments
BMI	Mass ÷ Height²	Health section
Lincoln Index	(n₁ × n₂) ÷ m	Ecology estimation
Simpson’s Index	1 − Σ(n/N)²	Biodiversity

IGCSE Economics Formula Sheet

IGCSE Economics has a surprising number of formulas and calculations that students must master. These quantitative skills often make the difference between a good grade and a great one.

Price Elasticity of Demand (PED)

One of the most important formulas in IGCSE Economics:

PED = Percentage Change in Quantity Demanded ÷ Percentage Change in Price

Key points:

• PED is always negative (but often expressed as an absolute value)
• PED > 1: Elastic demand (quantity changes more than price)
• PED < 1: Inelastic demand (quantity changes less than price)
• PED = 1: Unitary elastic
• PED = 0: Perfectly inelastic
• PED = ∞: Perfectly elastic

Exam tip: Always state whether demand is elastic or inelastic after calculating, and explain the implications for the firm’s revenue.

Price Elasticity of Supply (PES)

PES = Percentage Change in Quantity Supplied ÷ Percentage Change in Price

Key points:

• PES is always positive (supply curves slope upward)
• PES > 1: Elastic supply
• PES < 1: Inelastic supply
• Factors affecting PES: time period, spare capacity, availability of raw materials, stock levels

Percentage Change (Economics Context)

The building block for elasticity calculations:

Percentage Change = (New Value − Original Value) ÷ Original Value × 100

Total Revenue

Total Revenue = Price × Quantity Sold

Relationship with PED:

• If demand is elastic (PED > 1): Lowering price increases total revenue
• If demand is inelastic (PED < 1): Raising price increases total revenue
• If PED = 1: Revenue remains unchanged regardless of price changes

Profit Formulas

Profit = Total Revenue − Total Cost

Total Revenue = Price per Unit × Quantity Sold

Total Cost = Fixed Costs + Variable Costs

Average Cost = Total Cost ÷ Quantity Produced

GDP and Economic Growth

GDP (Gross Domestic Product) = Total value of all goods and services produced in a country in one year

Economic Growth Rate = (GDP This Year − GDP Last Year) ÷ GDP Last Year × 100

GDP per Capita = GDP ÷ Total Population

Exam tip: Always distinguish between nominal GDP (current prices) and real GDP (adjusted for inflation) when discussing economic growth.

Inflation Rate

Inflation Rate = (CPI This Year − CPI Last Year) ÷ CPI Last Year × 100

Where CPI = Consumer Price Index

Unemployment Rate

Unemployment Rate = (Number of Unemployed ÷ Total Labour Force) × 100

Note: The labour force includes only those of working age who are either employed or actively seeking employment.

Balance of Trade

Balance of Trade = Value of Exports − Value of Imports

• Trade Surplus: Exports > Imports (positive balance)
• Trade Deficit: Imports > Exports (negative balance)

Exchange Rate Calculations

When calculating the effect of exchange rate changes:

Amount in Foreign Currency = Amount in Domestic Currency × Exchange Rate

Amount in Domestic Currency = Amount in Foreign Currency ÷ Exchange Rate

Exam tip: Always specify which currency you’re converting to and from. State whether the currency has appreciated (increased in value) or depreciated (decreased in value).

Terms of Trade

Terms of Trade Index = (Index of Export Prices ÷ Index of Import Prices) × 100

• Terms of Trade improving: Export prices rising relative to import prices
• Terms of Trade worsening: Import prices rising relative to export prices

Tax Revenue

Tax Revenue = Tax Rate × Taxable Amount

For specific (unit) taxes: Tax Revenue = Tax per Unit × Quantity Sold

Consumer and Producer Surplus

While often shown graphically, students should understand:

• Consumer Surplus = Maximum price consumers are willing to pay − Actual price paid (summed across all units)
• Producer Surplus = Actual price received − Minimum price producers are willing to accept (summed across all units)

Economics Formula Quick Reference Table

Formula	Equation	Topic
PED	%ΔQd ÷ %ΔP	Elasticity
PES	%ΔQs ÷ %ΔP	Elasticity
Total Revenue	P × Q	Firms
Profit	TR − TC	Firms
Average Cost	TC ÷ Q	Firms
GDP Growth	(GDP₁ − GDP₀) ÷ GDP₀ × 100	Macroeconomics
Inflation Rate	(CPI₁ − CPI₀) ÷ CPI₀ × 100	Macroeconomics
Unemployment Rate	Unemployed ÷ Labour Force × 100	Macroeconomics
Balance of Trade	Exports − Imports	International Trade
Terms of Trade	(Export Price Index ÷ Import Price Index) × 100	International Trade

How to Use These Formula Sheets Effectively

1. Don’t Just Memorise — Understand

For each formula, make sure you understand:

• What each variable represents
• When and why the formula is used
• How to rearrange it for different unknowns
• What the result tells you in context

2. Practise With Past Paper Questions

The best way to solidify your understanding of these formulas is to use them in exam-style questions. Work through IGCSE past papers to see how formulas are tested in real exams.

3. Create Your Own Summary Cards

While this guide provides a comprehensive reference, creating your own condensed formula cards helps with memorisation. Write each formula, an example calculation, and a one-line explanation of when to use it.

4. Link Formulas to Concepts

In Economics especially, formulas don’t exist in isolation. For example, understanding PED isn’t just about the calculation — it’s about explaining how elasticity affects business decisions, government tax policy, and market outcomes.

5. Check Units and Show Working

In both Biology and Economics, marks are awarded for:

• Correct units (μm, %, currency symbols)
• Clear working shown step by step
• Appropriate rounding (usually 1-2 decimal places)
• Correct interpretation of the result

Common Exam Mistakes to Avoid

Biology Formula Mistakes

• Forgetting unit conversions in magnification calculations (mm to μm)
• Mixing up image size and actual size in the magnification formula
• Forgetting the ×100 in percentage calculations
• Not showing the balanced equation when only the word equation is recalled
• Confusing aerobic and anaerobic respiration products

Economics Formula Mistakes

• Forgetting PED is negative (or not explaining when using absolute values)
• Confusing elastic and inelastic — elastic means quantity changes MORE than price
• Using the wrong base value in percentage change calculations
• Not linking calculations to economic analysis — always explain what the number means
• Mixing up GDP and GDP per capita in living standards discussions

Additional Study Resources

These formula sheets are most effective when combined with comprehensive study materials. Here’s how to build a complete revision toolkit:

Revision Notes

Detailed notes for every topic provide the conceptual framework that gives formulas meaning. Tutopiya’s learning portal offers structured revision notes for all IGCSE Biology and Economics topics.

Practice Questions

Beyond past papers, topic-specific practice questions let you drill individual formulas until they become second nature.

Expert Tutoring

If you’re struggling with any of these formulas or their applications, working with an experienced tutor can make a huge difference. An IGCSE Biology or Economics tutor can walk you through calculations step by step and help you understand the underlying concepts.

Frequently Asked Questions

Are these formulas provided in the IGCSE exam?

For Biology, most formulas are not provided — you must memorise them. The magnification formula and sampling formulas should be learned by heart. For Economics, formulas are also not provided in the exam paper.

Which Biology formulas are most commonly tested?

The magnification formula and percentage change appear most frequently. Photosynthesis and respiration equations are also commonly tested, particularly in Paper 2/3 structured questions.

Do I need to memorise all the Economics formulas?

Yes. PED, PES, percentage change, profit, total revenue, and GDP growth are the most commonly tested. Understanding how to calculate and interpret these is essential for achieving top grades.

How should I revise these formulas?

Use a combination of:

1. Writing them out repeatedly
2. Practising with past paper questions
3. Teaching them to someone else (or explaining them aloud)
4. Using flashcards for quick daily review

Achieve Top Grades in IGCSE Biology & Economics

Mastering these formulas is a crucial step toward exam success. Combined with thorough content knowledge and strategic past paper practice, these calculations can significantly boost your grades.

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