The Math of Weight Watchers Points Plus

by -Paul-H- | | CC BY

Laura over at Math For Grownups wrote an article on the math behind the points system that Weight Watchers uses.

It was interesting. But since I didn’t do Weight Watchers, I merely found it a fun novelty. Until…

I joined Weight Watchers last week.

I was inspired by a combination of Fitarella’s 12 in 12 super motivational plan, Laura’s “How Many Points Is That?” article and my Ma declaring, “This is the last diet I will ever pay for!”

The points are fun to count and add and play with. After all, it’s math.

But I’m an electronic girl. So I downloaded the Weight Watchers iPhone app and began to plug in my food numbers there.

But the math isn’t quite what the math is supposed to be.

Like Laura said:

Instead of counting just calories, we’re considering four components of our food: protein, fiber, carbohydrates and fat.

Which means that all four of these bits go into a fun (and probably secret) math formula to arrive at the final number of official POINTS for a food.

Which was good with me. Until Ma recommended a great 1-point bread.

1-point for her, that is.

Apparently the iPhone app uses the decimals! Which means…

This 1-point bread is really more than one point!

The points, according to the iPhone app, go like this:

  • 1 slice = 1 point
  • 2 slices = 3 points (excuse me?)
  • 3 slices = 4 points
  • 4 slices = 6 points (really?)
  • 5 slices = 7 points
  • 6 slices = 8 points
  • 7 slices = 10 points (now you’re really getting on my nerves)
  • 8 slices = 11 points
  • 9 slices = 13 points
  • 10 slices = 14 points (*sigh*)

So what’s that about?

Shafting me out of points, is what!

Clearly the iPhone app uses the decimals that the paper version rounds to.

So from the information above, can you do the math? Can you figure out exactly how many points the Weight Watchers app assigns to a slice of this so-called 1-point bread?

You could put together a fancy math formula.

But that would be painful (yup, it’s as painful for you and me as it is for the kids – remember that).

Or you could just do some trial and error.

Here’re the assumptions:

  • Weight Watchers rounds like normal people. If it’s .5 or more, they round up. If it is .4 or less, they round down.
  • A slice of bread is more than one point. If it wasn’t, I wouldn’t be so mad.
Now to go in for the guesses:

Guess #1: A slice of bread is 1.2 points.

Does this work? If so, you can stop and go have a 2-point beer*, if not, continue.

How do you check it? See if it works in the “chart” above:

  • 1 slice = 1.2 point
  • 2 slices = 2.4 points YIPES!

This doesn’t work. 2 slices have to round up to be 3 points. This would round down to 2 points.

So on to the next guess:

Guess #2: A slice of bread is 1.3 points.

Check it in the “chart”:

  • 1 slice = 1.3 points
  • 2 slices = 2.6 points (good to go! this rounds up to 3 points)
  • 3 slices = 3.9 points (sweet! 3.9 rounds to 4 points)
  • 4 slices = 5.2 points (ARG! this shuts it down)

4 slices is supposed to be 6 points. So it needs to be at least 5.5 points.


Guess #3: A slice of bread is 1.4 points.

Check it in the “chart”:

  • 1 slice = 1.4 points ~ 1 point
  • 2 slices = 2.8 points ~ 3 points
  • 3 slices = 4.2 points ~ 4 points
  • 4 slices = 5.6 points ~ 6 points
  • 5 slices = 7.0 points = 7 points
  • 6 slices = 8.4 points ~ 8 points
  • 7 slices = 9.8 points ~ 10 points
  • 8 slices = 11.2 points ~ 11 points
  • 9 slices = 12.6 points ~ 13 points
  • 10 slices = 14.0 points = 14 points


You can use this with your kids!

by dno1967b | | CC BY

Okay, you might not want to share dieting things with kids. But you can share the “Dirty is better than pain” philosophy:

Why go through the pain of variables and formulas, when you can get your hands dirty with trial and error?

And guess what – if the kids are confident with the trial and error, they might someday see if they can generalize it themselves. Which means they could come up with a formula – on their own!

What do you think? Do you use formulas for your everyday math? Or do you “dirty>pain” it? Can you teach this to your kids?

Share your thoughts in the comments and make sure you tweet it out too!

*Note that the 2-point beer is also more than 2 points! #ARG

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