Life expectancies have been rising by up to three months a year since 1840, and there is no sign of that flattening. Gratton and Scott draw on a 2009 study to show that if the trend continues, more than half the babies born in wealthier countries since 2000 may reach their 100th birthdays. With a few simple, devastating strokes, Gratton and Scott show that under the current system it is almost certain you won’t be able to save enough to fund several decades of decent retirement. For example, if your life expectancy is 100, you want a pension that is 50 percent of your final salary, and you save 10 percent of your earnings each year, they calculate that you won’t be able to retire till your 80s. People with 100-year life expectancies must recognise they are in for the long haul, and make an early start arranging their lives accordingly.

Life expectancy has increased rapidly since the Age of Enlightenment. In the early 19th century, life expectancy started to increase in the early industrialized countries while it stayed low in the rest of the world. This led to a very high inequality in how health was distributed across the world. Good health in the rich countries and persistently bad health in those countries that remained poor. Over the last decades this global inequality decreased. No country in the world has a lower life expectancy than the countries with the highest life expectancy in 1800. Many countries that not long ago were suffering from bad health are catching up rapidly.