Kikie,
Why do you want to stop and start? If your goal is 150 then why not go all the way with IP in one shot? The thing is you are already on the train. It is much harder to get on the train when you are comfortable with where you are. You may be anxious to get IP done with but for losing weight there isn't anything out there that'll get you where you're going with less hassle.
I am almost embarrassed of how many diets I've been on. Some have been better than others but when it comes to quick weight loss and maintaining that weight loss well, for me IP really is the way. Period. I lost more after hitting maintenance by watching my caloric & carbohydrate values. But I would gain a bit with the free day so it was almost always a wash.
I started looking for a diet plan to lose slowly with. I can't really say whether they would work or not because with each of them I would spin off and not follow through. Don't know whether it's because I'm so indoctrinated by IP or because?? Following IP maintenance works. Unfortunately, for me trying to follow anything else does not. I'm slowly coming around to accepting this. You're not in ketosis in maintenance. And if you skip the free day and watch your calorie count you'll lose. But it is really hard to give up that treat day once you've had it. And it 'keeps the body guessing' so that you don't have to continually lower your calorie count to maintain. But if you spread it out to once every 10-14 days rather than once every seven throw in a phase 1 day each week. It all depends. IP maintenance can definitely be 'tweaked' so that you lose and it is by far the safest (no weight gain!!) route to take. I really can't recommend another program...
Sorry for being clear as mud but that's been my personal experience...

I cant really imagine why you wouldnt just do the extra 20# now on IP and get it over with...a month or month and a half or so and you would be there.

But thats just me...I know I can get away with the weight I am at right now but I know I will be much happier at 20# less so Im doing it all right now. The diet is safe and effective...oh yes EFFECTIVE that was key to me...Why struggle with another plan that may not work. Where will your motivation come from after the big weekly losses on IP?

I know that did not in any way answer your question, but just offering my opinion...And...I didnt have an answer for you lol

I was actually debating this same thing since I am 5# from goal and want to start phasing off for a vacation in a month. I plan on working out (P90x) in maintenance, but I know the less fat I have when I start that, the sooner I will see results. I just don't want to short myself or feel let down if I don't meet my goal. Its hard because I'm actually stoked to run and do hard work outs.
My advice is, wait it out- when you see that big loss week you will get stubborn. At least that's what happened to me yesterday!

Thanks for the post, I and many fellow IPers I think have the same question/struggle.

Sounds like you are wanting an excuse to stop early. You will just be cheating on yourself. Finish your weight loss with IP!!! The last 10 pounds seem to be hanging on for me, so I am getting used to it coming off slowly right now. Don't cheat yourself out of your goal.

A lot of people probably will not agree with me on this but that's ok.

I lost a good amt on IP and hit my goal of 120 and phased out. Then 2 days after entering maintenance I went on vacation and gained about 7-8ish pounds. After going back on IP and trying to lose the vacation weight I decided I was done with ketosis and the way it affected me. I couldn't stay on program for more than a few days and kept on sabatoging myself. This was just my experience. Many have done it. Restrictions dont work well for me. I havent gone out and eaten all kinds of bad things because I can now but I no longer have the urge to because I can if I want. It's weird, i know. To me, IP gave me the structure and willpower. Now i'm ready to fly on my own.

I decided to try out calorie counting with an emphasis on whole foods. No "100 calorie packs" and barely any processed foods. I'm losing consistently and loving it. I exercise daily and find it to be helping tighten up my weak spots. Again, this is just my experience.

IP does work. But it's not for everyone. Don't be afraid to go off and try something else. Many people have success with all different types of diets/weight loss plans. If you decide you dont like whatever you decided to try then you can always go back on IP.

That's just my $.02

Also, a similar question was asked on the calorie counting boards here. A couple more opinions posted there.

Well, this is kind of not an apples-to-apples comparison .... but I am planning to do IP to goal and maintain for a few months....THEN plan on baby #2. <Fingers crossed> During pregnancy I do plan on moving toward a more calorie counting/whole foods way of eating, taking pregnancy considerations into account of course. I don't want to blow up like I did with baby #1, as that is why I have so much to lose on IP now! But also, you don't really "diet" when you are pregnant, but will still be watching what I eat and monitoring it with my OB.

Of course there are ways! IP is a great program, but it is not the be all, end all to losing. What you learn while on IP and during your transition Phases will become the foundation to life after IP. That said, some suggestions for post-IP would be healthy, whole foods prepared well and eaten in moderation. Fresh veggies on hand ALWAYS ALWAYS. And IMO, exercise will be the biggest factor in dropping those last few lbs and maintaining a strong, lean body.

Your choice. But I would stay the course. I've never lost weight this fast and easily.

I am getting close to my goal but probably going to stay on longer

Wow way to go on your loss! And to keep going... hats off to you

Hey, kudos to you on your 170# weight loss in a year!

Yeah that is freaking awesome. I want to be there in ten more months saying I've lost 170#'s, that will still be 80#'s from my goal but sooooo much smaller and lighter. Actual I want to say I've lost at least 171# in a year so I am finally below 300#'s! Its been a decade since I've been under three bills!