Do implementation intentions work? Evidence on if–then plans

Specific if–then plans can help people carry out intentions, but their average benefit is less certain and less uniform than familiar success stories suggest. A large review covering 642 independent tests found positive effects overall, with substantial variation and evidence of publication bias. Methods that adjust for that bias produced smaller estimates, and how much smaller depended on the method. The review also pooled behavior, cognitive performance, feelings and social judgments, so its overall result is not an estimate for behavior alone. Sheeran, Listrom and Gollwitzer, published online 2024.

Think of an implementation intention as a way to link something you intend to do with a situation you will recognize. It does not supply every missing ingredient of behavior. A plan cannot create time, access or a skill that a person lacks, and writing one does not show that the person wants the outcome enough to pursue it.

What the plan adds

A goal states an outcome: “I want to keep better project notes.” An implementation intention links a cue to a response: “If the project meeting ends, then I will open the notes and write the next action before switching tasks.”

In this hypothetical example, the plan specifies a moment the person can recognize and an action they can perform. The response is more concrete than “be organized.”

The name matters because studies of planning do not always test the same thing. Some ask people to form an explicit if–then connection. Others ask them to choose a date and time. Still others combine planning with a separate exercise about goals and obstacles. These approaches may overlap, but evidence for one package does not identify the effect of every component.

The 642-test review distinguished contingent if–then plans from other planning formats. Benefits were generally larger for contingent plans, when participants were highly motivated, and when plans were rehearsed. Those patterns describe differences across the assembled studies; they do not provide a guaranteed formula for any individual. Sheeran, Listrom and Gollwitzer, published online 2024.

Children are a separate question. A 2026 meta-analysis by Jasmin Breitwieser and Tilman Reinelt, limited to children with an average age under 13, combined 52 effects from 42 studies involving 12,957 children. The pooled effect was g=0.31, a small-to-medium difference in standard-deviation units, with substantial variation across studies. The authors found signs of publication bias, but the adjustments disagreed: one method roughly halved the estimate, to 0.15, while a selection model put it at 0.38. The result supports testing if–then plans with children; it does not tell an adult program what to expect. Breitwieser and Reinelt, 2026.

A workplace flu-shot result and its size

A workplace vaccination study by Katherine Milkman and colleagues shows how a small change to a reminder can affect a concrete action. Employees received information about free workplace flu clinics. Some were also prompted to write down a date, or a date and time, for attending.

About one-third of the control group was vaccinated. The date-and-time prompt raised vaccination by an adjusted 4.2 percentage points relative to the standard reminder. The date-only prompt did not produce a statistically reliable increase. Milkman and colleagues, 2011.

This is a meaningful result from a specific situation: an available service, a short opportunity to use it, and a prompt attached to information that employees were already receiving. The intervention helped some additional people act. It did not make everyone comply, and it did not remove the need for the clinic itself.

The study also illustrates why a percentage-point gain can be worth having. A few additional actions per hundred people may matter when an intervention is cheap and the action has value. That is a different claim from saying a planning prompt radically transforms motivation.

Why another plausible planning prompt did not help

Mariana Carrera and colleagues later tested a scheduling prompt with 877 gym members. Participants in the intervention chose days and times to exercise over the next two weeks. They engaged with the planning task, but the study did not find an increase in gym attendance. Carrera and colleagues, 2018.

This result does not directly refute every if–then plan: choosing a schedule is not the same as forming a plan that links a cue to a response. It does challenge the broader assumption that asking people to plan when they will act is usually enough.

It also poses a practical question. Was the problem forgetting an intended action, finding a suitable opportunity, sustaining motivation, or something else? A reminder to decide on a time may address one of these obstacles while leaving the others in place. The comparison between the gym and vaccination studies does not isolate which difference explains their results. It shows why the successful example should not be carried into a new setting without testing.

The broader review also found that some outcome categories, including vaccination and voting, had uncertainty intervals consistent with no average benefit. A positive individual study and an uncertain category-level result can coexist. Sheeran, Listrom and Gollwitzer, published online 2024.

How to use a plan and test it

Start with an action that someone actually intends to take. Then ask what recognizable event could prompt it, whether the action is feasible at that moment, and what will count as completion. These are useful design questions. Answering them does not promise an automatic habit.

For example, “If I finish a customer call, then I will record the agreed next step before opening my inbox” gives the person a clear opportunity to act. But if the call system immediately routes another call, the plan may be impractical. Changing the workflow could matter more than strengthening the wording.

The same distinction applies to public programs. Asking someone to plan an appointment does not solve unavailable appointments or an inaccessible booking process. A planning prompt can be evaluated as one addition to a functioning service. It should not be used to explain away obstacles that the service creates.

When evaluating a prompt, measure the intended behavior. Did the appointment happen? Were the notes completed? Did attendance change? A well-written plan, a favorable survey response and confidence that the plan will help are not interchangeable with action. Compare the prompt with what people would otherwise receive, including any reminders or support already in place.

Implementation intentions remain a reasonable tool for helping people follow through on feasible goals. The evidence favors modest, context-sensitive expectations. Use the plan to make an intended action more concrete, then check whether the action changes. The research does not support treating planning as a substitute for motivation, resources or a workable environment.