How to tell if a habit is actually working

Short answer: compare. Rate how you feel a couple of times a day, at the moment, not from memory. After a few weeks, put the days you did the habit next to the days you didn’t, and look at the same day and the day after. If there’s a gap and it holds up as more days come in, the habit is paying you back.

That’s the return on a habit. Every habit costs you something: twenty minutes, an earlier alarm, the coffee you skip. Most habit trackers only record whether you paid that cost today. The return is how you felt afterwards, and almost nobody writes that down.

Signal	What it tells you	What it can’t tell you
A streak	You kept doing it	Whether it helped
How you remember the week	How the week feels now	How each day felt at the time
Days with vs days without	Whether habit days feel different	Why they do
The day after	Whether the gap lasts, and which came first	Whether something else caused it

A streak measures effort, not effect

Streaks are good at one thing: keeping you going. In seven studies, Silverman and Barasch (2023) found that when a behaviour log showed an intact streak, people kept up the behaviour more than when it showed a broken one. The effect didn’t depend on what people had actually done, only on how the log displayed it. People treat keeping the streak as a goal in itself.

That’s useful for motivation, but it means the streak can quietly become the point. You can keep a 60-day streak going on something that does nothing for you, and quit something that helps because you missed a Tuesday.

The missed Tuesday matters less than the counter suggests. In the best-known study of how habits form, Lally and colleagues (2010) had 96 volunteers repeat one daily behaviour, such as drinking a bottle of water with lunch or going for a 15-minute run, for 12 weeks. Missing a single day didn’t materially affect how automatic the habit became. And for the participants whose data fitted the model, it took a median of 66 days for the habit to level off, with estimates from 18 to 254 days. That’s far longer than the often-quoted 21 days, and too long to judge a habit by its first week.

Your memory is a poor judge

The other way to decide whether a habit helps is to think back over the last few weeks. The trouble is that recall is bent by what stood out and by how you feel while you’re remembering. That’s why researchers who study everyday life prefer to ask people how they feel right now, often several times a day, rather than how their week went. It’s called ecological momentary assessment, and Shiffman, Stone and Hufford’s 2008 review makes the case for it: global, after-the-fact reports suffer from recall error and miss how feelings change from one moment and place to the next.

You don’t need a research protocol to borrow the idea. A rating you make on the spot, a couple of times a day, beats a judgement you make at the end of the month.

Two numbers are enough

How do you rate a feeling quickly? Psychologists have a well-worn answer. In 1980, James Russell showed that people’s words for feelings arrange themselves around two dimensions: how pleasant or unpleasant a feeling is, and how energised or sleepy. Tired and calm are both low-energy, but one feels better than the other. Anxious and excited are both high-energy, and feel very different.

So two quick numbers, how good and how energetic, capture most of what a check-in needs. Ten seconds each time, and you have something you can compare across days.

Compare the days you did it with the days you didn’t

Say you went for a 20-minute walk on 12 of the last 30 days. Average your mood on those 12 days, then on the other 18. The difference is the return on the walk, at least so far.

Then look one day later. The same-day number can run backwards: on days you already feel good, you’re more likely to go for a walk or call a friend. If the day after a walk is also better than the day after a day without one, the walk at least came before the better mood. It’s still not proof of cause, but it’s a much better sign than a same-day link alone.

Your own numbers matter more than anyone else’s. In the Day Reconstruction Method study (Kahneman et al., 2004), 909 working women in Texas rated each episode of the previous day; socialising and relaxing were among the most enjoyed, and the commute the least. That’s a fine starting point for guessing what might help. But it’s an average across hundreds of people, and only your own days can tell you what works for you.

Four things that fool the comparison

1. The weekend. In Gallup data from 340,000 people in the United States, mood was better on Fridays and through the weekend, while there was little sign of a “Blue Monday” (Stone, Schneider and Harter, 2012). If you mostly do a habit on weekends, it gets credit for the weekend.
2. Starting in a bad patch. People often start a habit when things feel off. An unusually bad stretch tends to be followed by a more ordinary one whatever you do, which statisticians call regression to the mean (Barnett, van der Pols and Dobson, 2005). The habit gets the credit for a recovery that was coming anyway.
3. Something else changed. A holiday, a deadline, a cold, a new job. Your numbers can’t tell these apart from the habit unless you notice them.
4. Too few days. With four habit days and four without, one great or awful day moves the whole average. Wait for more data before you believe a number, especially a big one.

None of these makes the comparison useless. They’re why a single week is a hint, a few weeks are evidence, and a “too early to tell” is an honest answer rather than a failure.

Run a one-week experiment

If you’d rather test one habit deliberately than wait for the numbers to build up:

1. Pick one habit. Change two things at once and you can’t tell which one did it.
2. Check in for a normal week first. That’s your baseline.
3. Do the habit every day for seven days. Keep the rest of your routine as normal as you can.
4. Keep checking in at about the same times. Mood shifts during the day, so keep the timing comparable.
5. Compare the two weeks, and check the four traps above. A small gap means too early to tell. If it looks promising, keep going and let the days-with versus days-without comparison build up.

This is for noticing patterns in ordinary days, not for diagnosing or treating anything. If low mood lasts for weeks or gets in the way of daily life, talk to a doctor.

Where Moments fits

I built Moments to do this bookkeeping for me. The check-in is the two-number rating above: you drag a sun across a sky, up for more energy and right for feeling better, and pick what you’re doing. It takes about five seconds.

Habit ROI is the comparison from this post. For each habit, it averages your mood on the days you logged it and on the days you didn’t, same-day and next-day, and adds sleep and heart-rate variability if you connect Apple Health. It won’t show a measured number until a habit has been logged on at least eight days. It reports the difference, not a cause, and it says so.

7-Day Experiments are the one-week test: Moments compares the week before you started with the week of the experiment, and gives you a verdict of worked, didn’t, or too early to tell.

Check-ins and 7-Day Experiments are free. Habit ROI is part of Moments Plus, an optional subscription. There’s no account, and your moments stay on your device.

Sources

• Silverman, J. and Barasch, A. (2023). On or Off Track: How (Broken) Streaks Affect Consumer Decisions. Journal of Consumer Research, 49(6), 1095–1117.
• Lally, P., van Jaarsveld, C. H. M., Potts, H. W. W. and Wardle, J. (2010). How are habits formed: Modelling habit formation in the real world. European Journal of Social Psychology, 40(6), 998–1009.
• Shiffman, S., Stone, A. A. and Hufford, M. R. (2008). Ecological momentary assessment. Annual Review of Clinical Psychology, 4, 1–32.
• Russell, J. A. (1980). A circumplex model of affect. Journal of Personality and Social Psychology, 39(6), 1161–1178.
• Kahneman, D., Krueger, A. B., Schkade, D. A., Schwarz, N. and Stone, A. A. (2004). A survey method for characterizing daily life experience: The day reconstruction method. Science, 306(5702), 1776–1780.
• Stone, A. A., Schneider, S. and Harter, J. K. (2012). Day-of-week mood patterns in the United States: On the existence of ‘Blue Monday’, ‘Thank God it’s Friday’ and weekend effects. The Journal of Positive Psychology, 7(4), 306–314.
• Barnett, A. G., van der Pols, J. C. and Dobson, A. J. (2005). Regression to the mean: what it is and how to deal with it. International Journal of Epidemiology, 34(1), 215–220.