Relatively few workers take full advantage of retirement savings plans their employers offer and, among those who participate in employer-sponsored retirement plans, contribution rates vary considerably over time. Using a newly available Census dataset that combines administrative earnings records with survey reports, we find that workers raise their contribution rates when they achieve key milestones in life, such as the birth of a child or the purchase of a home. Potential negative shocks to income and increases in current consumption needs, however, do not lead workers to curtail their contributions. [View the corresponding press release]