Lower birth-rates and longer lives lead to population aging, which matters for many reasons, but first and foremost because of the costs of retirement. These costs are borne principally by the government and funded through taxes on the working-age population. The old-age-dependency ratio – that is, the population aged 65 and over divided by the population aged 15 to 64 – is a key indicator of population aging. Other things being equal, the tax rate for pensions will be proportional to this ratio. In the developed world, this ratio rose from .12 in 1950 to .21 today, and is estimated to increase to .44 in 2050. If, in the developed countries, the elderly in 2050 are to receive the level of benefits given to the current elderly, then the level of payroll taxes needed to fund government pensions will more than double by 2050. Due to higher fertility and immigration, the US population is projected to remain younger than those of other OECD countries, and the pension problem will be less severe. Health costs, however, pose an even more difficult problem due to the socialized health-care system for the elderly in the US. As the population ages and spending per elderly person rises, government spending on health care will likely soar.