Birth Lottery is a game, but behind it there's a small model that runs on real data. In this article, we explain in plain language how that model is built: how the country is drawn, where the chance of dying comes from, how events and decisions work, and how the score and percentile are calculated. At the end, we also spell out the simplifications the model makes on purpose, because knowing what it doesn't do is part of understanding it.

1. The dataset

The game has 70 countries. For each country, we use these values: annual births, life expectancy at birth, fertility rate (UN World Population Prospects 2024), income per person (at purchasing power parity), under-5 mortality rate and urban population share (World Bank, World Development Indicators). The values are from around 2022-2023 and were entered in approximate, rounded form. Some countries are also flagged as "conflict zones"; this flag raises the chance of war-related events. The 70 countries on the list cover most of the world's births, but not all of them: annual births in the dataset add up to about 116 million, against a world total of about 132 million.

2. The birth draw

When you roll the dice, the program lines up the annual births of the countries on the list and picks a random point. Countries with more births take up a bigger stretch of that line. That's why your chance of being born in India is about one fifth of all births on the list, or about 20 percent. The chance of being born in Turkey is about 0.8 percent, in the UK about 0.6 percent, in Japan about 0.6 percent and in Chad about 0.6 percent. The "If you were born right now" list on the home page shows the eight most likely countries according to these odds.

Once the country is drawn, the other starting traits are set:

  • Sex: about 51 percent boys, 49 percent girls.
  • Family income bracket: from 1 (poor) to 5 (well-off), with equal probability.
  • City or countryside: according to the country's urban population share.
  • Number of siblings: according to the country's fertility rate. In Chad you'll often have many siblings, in South Korea few.
  • Mother's age: random between 18 and 32.

The whole draw comes from a single seed value. Two games that start with the same seed produce the same person; that's how challenges and "Life of the Day" work. When your friend opens the link, they're born in the same country, into the same family, with the same number of siblings. The differences come from the decisions made after that.

3. The chance of dying

The chance of dying is made up of two parts.

Childhood: from real mortality rates

For the first year, the chance of dying is about 72 percent of the country's under-5 mortality rate. In Chad, that comes to about 77 per thousand, or roughly 7.7 percent. For each year between ages one and four, the chance of dying is taken as about 7 percent of the under-5 mortality rate; in Chad, that works out to about 7.5 per thousand per year. This split is a simple approach based on the fact that infant deaths make up most child deaths. In countries like Japan, where child mortality is very low, these years are almost risk-free.

Adulthood: the Gompertz curve

After age five, the chance of dying is set by a formula called the Gompertz curve. The idea behind this formula, long used for human mortality, is simple: the risk of death rises exponentially with age. When you're young, the risk is very low; as you get older, it climbs quickly. The curve has two settings: the rate of increase is held constant, while the starting point is shifted according to the country's life expectancy. The target average lifespan is calculated by adding the family income bracket effect (about 1.8 years per bracket) and a small correction to the country's life expectancy. That way, characters born in Japan land at around 84 years on average, and those born in Chad much lower. The curve is still random, though; some characters live far above the average and some far below.

Causes of death (car accident, heart attack, dying in your sleep and so on) are fictional texts chosen by age; they don't reflect the real distribution of causes of death.

4. Events

Every year, the game runs a probability check for events that fit the character's age and situation. Some events are the same for everyone (first steps, first word), while others depend on the country and the family:

  • The chance of an illness with a high fever rises with the country's child mortality rate.
  • The chance of getting vaccinated depends on the country's level of development.
  • Famine and water-carrying events appear in poor families and in rural areas of low-income countries.
  • Events like promotions, layoffs and buying a home depend on having a job and on wealth.
  • Characters born in a conflict zone may face war events.

Milestones like going to school, getting into university and retiring are also shaped by the country's income per person and the family's income bracket. That way, a poor child and a well-off child born in the same country can take different paths. The event texts are fiction; they don't belong to any real person.

5. Decisions

At seven points in life, the decision is left to you: what to do at break time, which path to take after school, moving abroad, marriage, a risky job offer, a health warning and free time in old age. Your choice has small effects on five indicators: health, happiness, knowledge, love and wealth. For some decisions, like the risky job offer, the outcome still depends on chance. The "Auto" button makes these decisions at random. Once you've seen the results, you can try different choices with the "Same start, again" button.

6. Score and percentile

When the life ends, the score is calculated from these components: the number of years lived (the biggest weight), the lifetime average levels of happiness, love, knowledge, wealth and health, and the badges earned. A score means nothing on its own, so a percentile is added next to it: the first time you reach the results screen, the program simulates 500 random lives from start to finish in the background and ranks your score among those 500 lives. "Better than 80 percent of lives" means that about 80 percent of those 500 lives scored lower than you.

Since these 500 lives are produced with the same draw, the percentile behaves like a real slice of the world: people born in long-lived countries usually end up in the top percentiles, and those born in countries with high child mortality in the bottom ones. Also, 500 lives is a small sample; the percentile can shift by a few points.

Limits and deliberate simplifications

  • National averages. The model represents each country with a single value. In reality, there are big differences between regions, ethnic groups and classes within a country.
  • 70 countries. Only 70 of the world's roughly 195 countries are on the list. Smaller countries were left out.
  • Fixed time. Life expectancy assumes that today's death rates will stay the same for a whole lifetime. In reality, medicine advances and countries change.
  • Event probabilities. The yearly probabilities of events are approximate values chosen for this game; they aren't exact statistics of real life.
  • Fiction. Names, event texts, causes of death and badges are written for entertainment and storytelling.
  • Score. The scoring carries a value judgment: a long life and happiness count as a "good life". Not everyone defines a good life that way.

In short, the model is a sketch of how much birthplace matters, not a photograph. The point of the sketch is to help you sense the differences hidden behind a national average. For the real data, the open data portals of UN WPP 2024 and the World Bank are the best place to start.

If you're curious about the data itself and the differences between countries, take a look at the life expectancy article. Ready? Roll the dice.