About

Annual counts, one loop, one caveat: age structure is still not projected.

What the page computes

Pick a country or enter your own values. The model adds annual births, subtracts annual deaths, and adds net migration to the starting population, once a year.

P(t+1) = P(t) + births − deaths + net migration

With China's 2026 inputs — 1.40828 billion people, 9.54 million births, 10.93 million deaths and 310,000 net emigration — the population falls by 1.70 million a year. Ten years gives about 1.391 billion.

Step	Calculation	Result
Births	9,540,000	+9,540,000
Deaths	10,930,000	−10,930,000
Net migration	310,000 net emigration	−310,000
Annual change	9,540,000 − 10,930,000 − 310,000	−1,700,000
End of year	1,408,280,000 − 1,700,000	1,406,580,000

Inputs and units

Country presets: 14 countries plus a world total. Values are 2023–2024 estimates from the UN World Population Prospects and national statistical offices, rounded to the nearest 10,000.
Units: population, births, deaths and migration can be entered in billions, millions, thousands or people. Changing the unit converts the number rather than changing its meaning.
Years: the start year is 2026–2035 and the horizon is 5–10 years. The table runs from the start year to the final year.
Births and deaths must be zero or positive. Net migration is signed: positive for immigration, negative for emigration.
The population is clamped at zero after each year. A negative population has no interpretation.
Recalculation happens on every keystroke and every change; there is no submit button.

What the result shows

Total change and the average annual change, both in people and as a percentage of the starting population.
Cumulative births, deaths and net migration over the whole period, not just the final year.
Annual growth rate (CAGR): the compound rate that would take the starting population to the final one over the chosen years.
Three views: a trend line, an age-shape illustration and a start-year age-structure pie chart.
Country data: a national overview for every preset; China adds emigration destinations and provincial birth and death rates.

What the model does not know

Age structure. The model has one population total, not age groups. It cannot represent population momentum or a bulge of elderly people. The pie chart shows the start year only.
Changing counts. Births, deaths and migration stay at the same annual number. In reality they move with the age structure, the economy and policy.
Migration by origin or age. Net migration is a single number applied to everyone.
Data quality. A national total is only as good as the registration and census system behind it, and migration is the least reliable of the four inputs.

Where the default values come from

Country totals, births, deaths and net migration come from the UN World Population Prospects 2024 and national statistical offices, rounded to the nearest 10,000. China's provincial birth and death rates are 2023 statistical-communiqué approximations; the emigration destination table uses UN international migrant stock and national censuses. These are starting points for a scenario, not an official series.

How the pages are built

Four static pages, shared stylesheets and one script, served from this domain. No framework, no third-party script, no analytics, no cookie. The projection is a single function with no dependencies, and the worked year above is the check used for a change.

Corrections

If a formula, a country value or a boundary is wrong, the fix belongs in the script, the country table and this page. The checks cover zero years, a one-year step, negative net migration, a zero-change case and the clamp at zero, so the table and the description cannot drift apart.