Research suggests that breaking overarching goals into more granular subgoals is beneficial for goal progress. However, making goals more granular often involves reducing the flexibility provided to complete them, and recent work shows that flexibility can also be beneficial for goal pursuit. We examine this tradeoff between granularity and flexibility in subgoals in a pre- registered, large-scale field experiment (N = 9,108) conducted over several months with volunteers at a national crisis counseling organization. A pre-registered vignette pilot study (N = 900) suggests that the subgoal framing tested in the field could benefit goal-seekers by bolstering their self-efficacy and goal commitment, and by discouraging procrastination. Our field experiment finds that reframing an overarching goal of 200 hours of volunteering into more granular subgoals (either 4 hours of volunteering every week or 8 hours every two weeks) increased hours volunteered by 8% over a 12-week period. Further, increasing subgoal flexibility by breaking an annual 200-hour volunteering goal into a subgoal of volunteering 8 hours every two weeks, rather than 4 hours every week, led to more durable benefits.