Healthcare takes a bigger share of Social Security benefits as you age. Many people expect that they will be able to live on less income in retirement. Some expenses clearly will fall for some (such as mortgage payments and commuting costs), but others may rise, and potentially increase over time (such as healthcare).
Based on current projections from HealthView Services, a 45-year-old couple will spend an average of 63% of their Social Security income on healthcare. But at age 87, that same couple will need 72% of their Social Security income to cover health-related expenses.