Life expectancy in Ancient Rome was from 20 to 30 years.

Demographically, the Roman Empire was an ordinary premodern state. It had high infant mortality, a low marriage age, and high fertility within marriage. Perhaps half of Roman subjects died by the age of 5. Of those still alive at age 10, half would die by the age of 50. At its peak, after the Antonine Plague of the 160s CE, it had a population of about 60–70 million and a population density of about 16 people per square kilometer. In contrast to the European societies of the classical and medieval periods, Rome had unusually high urbanization rates. During the 2nd century CE, the city of Rome had more than one million inhabitants. No Western city would have as many again until the 19th century.

When the high infant mortality rate is factored in (life expectancy at birth) inhabitants of the Roman Empire had a life expectancy at birth of about 25 years. However, when infant mortality is factored out, life expectancy is doubled to the late-50s. If a Roman survived infancy to their mid-teens, they could, on average, expect near six decades of life, although of course many lived much longer or shorter lives for varied reasons.

Although this figure relies more on conjecture than ancient evidence, which is sparse and of dubious quality, it is a point of general consensus among historians of the period. It originates in cross-country comparison: given the known social and economic conditions of the Roman Empire, we should expect a life expectancy near the lower bound of known pre-modern populations. Roman demography bears comparison to available data for India and rural China in the early 20th century, where life expectancies at birth were also in the low 20s.

About 300 census returns filed in Egypt in the first three centuries CE survive. R. Bagnall and B. Frier have used them to build female and male age distributions, which show life expectancies at birth of between 22 and 25 years, results broadly consistent with model life tables. Other sources used for population reconstructions include cemetery skeletons, Roman tombstones in North Africa, and an annuities table known as "Ulpian's life table". The basis and interpretation of these sources is disputed: the skeletons cannot be firmly dated, the tombstones show non-representative sample populations, and the sources of "Ulpian's life table" are unknown. Nonetheless, because they converge with low Roman elite survival rates shown in the literary sources, and because their evidence is consistent with data from populations with comparably high mortality rates, such as in 18th century France, and early 20th century China, India, and Egypt, they reinforce the basic assumption of Roman demography: that life expectancies at birth were in the low 20s.

As no population for which accurate observations survive has such a low life expectancy, model life tables must be used to understand this population's age demography. These models, based on historical data, describe 'typical' populations at different levels of mortality. For his demographic synopsis of the Roman Empire, Bruce Frier used the Model West framework, as it is "the most generalized and widely applicable". Because it is based on only one empirical input, the model life table can provide only a very approximate picture of Roman demography. On two important points, the table may seriously misrepresent the Roman situation: the structural relationship between juvenile and adult mortality, and the relative mortality rates across the sexes. In any case, Roman mortality should be expected to have varied greatly across times, places, and perhaps classes.

A variation of ten years would not have been unusual. A life expectancy range of between 20 and 30 years is therefore plausible, though it may have been exceeded in either direction in marginal regions.