How to use the simulator
The one control is the Stage slider, which runs from 1 to 5 in whole steps and starts at Stage 2.
The chart shows the birth rate (CBR) as a teal line and the death rate (CDR) as a navy line, both measured per 1,000 people per year on a 0–40 axis. A dotted coral line traces total population. The band for the current stage is shaded, and dots mark that stage's two rates.
The panel to the right shows the stage name, Birth rate (CBR), Death rate (CDR), Natural increase (per 1,000 and as a percentage), Population trend, and a description with example countries. These are the values for each stage:
- Stage 1, High Stationary: CBR 38, CDR 38, natural increase 0 (0.0%). Low and stable.
- Stage 2, Early Expanding: CBR 38, CDR 18, +20 (+2.0%). Rapid growth.
- Stage 3, Late Expanding: CBR 24, CDR 10, +14 (+1.4%). Growth slowing.
- Stage 4, Low Stationary: CBR 14, CDR 9, +5 (+0.5%). Stable or very slow.
- Stage 5, Declining: CBR 8, CDR 11, −3 (−0.3%). Shrinking.
These are typical values for each stage, not data for a particular country. The population curve is an index showing shape only: flat, then steep, then levelling off, then dipping slightly in Stage 5.
The key ideas
The crude birth rate and crude death rate are births and deaths per 1,000 people per year. The rate of natural increase ignores migration:
Dividing by 10 converts "per 1,000" into "per 100". The doubling time is roughly years (the rule of 70).
- Stage 1. High births and high deaths cancel out. No country is in this stage today.
- Stage 2. The death rate falls first, thanks to better food supply, clean water, sanitation and vaccines, while birth rates stay high. The widest gap produces the fastest growth.
- Stage 3. Birth rates fall as countries urbanize, children become an economic cost rather than farm labour, women gain education and paid work, contraception spreads and child mortality drops.
- Stage 4. Both rates are low and close together. Growth is near zero and the population is ageing.
- Stage 5. A later addition to the model. Fertility is very low and the older population raises the death rate, so deaths exceed births and the population shrinks without immigration.
The model is based on the experience of Europe and North America. Critics point out that it does not include migration, that today's developing countries reached low death rates much faster through imported medicine, and that it does not guarantee every country will move on to Stage 3. The epidemiological transition model follows the causes of death through the same stages.
Worked example
Problem: A country has a crude birth rate of 24 and a crude death rate of 10. Find its rate of natural increase and approximate doubling time, and place it in the DTM.
Step 1: Natural increase. per 1,000, so .
Step 2: Doubling time. years.
Step 3: Stage. The death rate is already low but the birth rate is falling and still well above it, so this is Stage 3. Set the slider to 3 and the panel shows the same figures: CBR 24 / 1,000, CDR 10 / 1,000 and natural increase +14 / 1,000 (+1.4%).
Step 4: Compare with Stage 2. Move the slider back to 2. Natural increase becomes +20 per 1,000, or 2.0%, so the doubling time drops to years. The birth rate is the same in Stages 1 and 2. What sets off rapid growth is the fall in the death rate.
Step 5: Look ahead. At Stage 4 the panel shows +0.5%, a doubling time of about 140 years. At Stage 5 the figure is negative, so the population never doubles. It shrinks unless immigrants make up the difference.
Common mistakes on the AP exam
- Saying population is lowest in Stage 5. Growth rate and population size are different things. Population is at its largest in Stages 4 and 5, even though growth is near zero or negative.
- Getting the order of the declines wrong. Deaths fall first (Stage 2), births follow (Stage 3).
- Forgetting to divide by 10. A natural increase of 14 per 1,000 is 1.4%, not 14%.
- Explaining a falling birth rate with medicine alone. Medicine mainly explains the Stage 2 drop in deaths. The Stage 3 drop in births needs social and economic reasons, such as urbanization, women's education and employment, and lower child mortality.
- Ignoring migration. The DTM tracks natural increase only. A Stage 5 country can still grow through immigration.
When the AP exam uses this
The demographic transition model is topic 2.5 in AP Human Geography, and it links to population pyramids (2.3), Malthusian theory (2.6), population policies (2.7) and ageing populations (2.9). Free-response questions often give birth and death rates or a pyramid and ask you to identify the stage, explain why the rates changed, or describe a limitation of the model.