Every once in a while someone emails me and asks something like, "I sit on the couch too much. I'm trying to be more active. How many days will it take before my new exercise routine becomes a habit? My friends tell me it will take about thirty
days, but I think it will only take 25. What do you think?"
After I get such a question, I walk across my oak-paneled office, open a hidden door, and follow the steps down to my secret lair. Among my five billion volumes, I find the book with questioner's name inscribed upon it. I consult a few tables and do some calculations. I have to factor in the person's age at the time she queried me, the particular habit she wants to acquire, and a few (thousand) other variables. Aha! 23.638 days! I rush back up to my computer . . .
On the other hand, it might have been easier to dash into my time machine to find out how long it took my questioner. I could then report back to her . . .
Of course, that kind of messing with laws of physics would create a temporal paradox that only a good Hollywood writer could ignore.
The foregoing was not meant to mock anyone in particular, except perhaps psychologists. I understand. You want to replace a bad habit with a new good habit and you want to know how long it will take. I'm sorry that I don't have a hard and fast answer for you.
Maybe one day we psychologists will be able to give everyone his or her magic number, but right now there's just no way. That's not to say that I have no information for you. You won't leave empty-handed. It's just that I have a fairly typical academic-psychologist-I'm-being-careful kind of answer: "It depends."
Some thoughts on the "depends":
1. What kind of habit are you trying to establish? Some will be easier to establish than will others. For example, if you've been eating the same fat-laden sugar-rich lunch for the past 10 years and you've decided to switch to salad, it's going to take some time. There will be setbacks. But, if you're "tweaking" some behavior of yours, the time to habit change will likely be much shorter. That's one of the reasons why I recommend that people take baby-steps when they are changing a behavior. You'll see some progress fairly quickly. You can solidify that progress and move on from there.
2. What are the benefits to continuing with your bad habit? We have bad habits because they give us short-term payoffs. It's that feeling of a juicy burger melting in our mouths, or gleefully sinking into the couch instead of schlepping to the gym. To be sure, you're not the biggest fan of yourself for having a bad habit, but you wouldn't have it if there weren't some benefit. I don't know too many people who regularly hit themselves over the head with a big stick. Although, some behaviors do come kind of close to that.
The more immediate and tasty the payoff, the harder it will be to break the bad habit and replace it with a good one.
3. How often/automatically do you perform the bad behavior? The more often/automatically you do it, the harder it will be to change it. After all, you have to be aware that you're doing something bad in order to replace it with something good.
That last point reminds me of the one of the steps for effective habit change: Repeat, repeat, repeat! It's like learning to drive a car. If you drive, you must have remarked to yourself how easy it is to motor along now compared to when you first learned. You don't have to coach yourself through every move (check my blind-spot, signal . . . ) You just do it. That's because of one thing and one thing only: Lots and lots of practice. Repeat, repeat, repeat.
You'll have to excuse me; I left the secret door open again. How many times do I need to remind myself . . .