Name: Keep the Diff
Author: Lee

A no buy challenge and a low buy challenge both aim to cut impulse spending. The difference is how much room you leave yourself. One draws a hard line. The other draws a smaller circle. People mix the terms up, and picking the wrong one is a common reason a challenge ends in February.

What a no buy challenge is

In a no buy challenge you do not purchase anything outside an agreed list. The list usually covers groceries, rent, utilities, transport, medicine and a few named exceptions. Everything else is a no for the length of the challenge, which might be a month or a year.

What a low buy challenge is

In a low buy challenge you still shop, but with limits. The limit might be an item count (one piece of clothing a month), a category cap ($40 a month on books), or a set of categories you cut while the rest stay open. The point is to buy deliberately instead of on impulse.

Low buy vs no buy, side by side

A general comparison. Challenge rules vary from person to person.

	No buy	Low buy
The rule	Nothing outside the allowed list	Limited amounts or items in chosen categories
Where it works best	Short stretches, or a clear reset	Longer stretches and ordinary life
Main strength	Simple. No decisions to make.	Flexible. Fewer days that feel like a test.
Main risk	One slip can feel like the whole thing failed	Limits drift upward without notice
What to track	Money kept by skipping	Money kept by buying less or paying less

Which one fits you

Choose a no buy if:

You want a clean reset and enjoy a clear rule.
Your spending is concentrated in a few categories, such as clothes or online shopping.
The challenge is short, like a no spend month.

Choose a low buy if:

You are planning a full year.
You have regular small needs, like replacing worn out basics.
A strict rule has made you give up before.

Plenty of people start with a no buy month and move to a low buy year. Both are fine ways to begin. For the wider set of terms, see no buy year, no spend month, low buy: what the terms mean.

Example low buy rules to copy

One new clothing item a month, and it must replace something or fill a gap on your list.
Books from the library first. Buy only after a second borrow.
No new decor. Rearranging what you own is allowed.
A $25 monthly allowance for anything outside the list, spent only after a seven day wait.
Every purchase over $50 waits a week before it is decided.

Example no buy rules to copy

I can buy food, bills, medicine and transport.
I can replace something that breaks, one for one.
My planned exceptions this year are a trip in June and two birthday gifts.

Tracking is where the two differ most

A no buy challenge fits a day counter, since a day either has a purchase or does not. A low buy challenge does not. Some days include a purchase that was well within your rules. A day count would call that a failure, though your rules allowed it.

Money is the better thing to track for both. Each time you decide, note what you were ready to spend and what you actually spent:

You wanted a $60 jacket and skipped it. Planned $60, actual $0. You kept $60.
You wanted a $60 jacket and bought a $25 secondhand one. Planned $60, actual $25. You kept $35.
You wanted a $12 book and borrowed it from the library. Planned $12, actual $0. You kept $12.

That is one subtraction, and it works for a strict no buy and for a flexible low buy in exactly the same way.

Doing it in Keep the Diff

Keep the Diff is built around that subtraction. Planned spend minus actual spend equals the Diff, and the Diff adds up by week, by month and toward a goal. A low buy purchase that came in under what you had planned is logged as a smaller Diff. A skip is logged as the full amount. A purchase you made and have no regrets about is simply logged. Nothing resets, and there are no streaks.

If you cannot decide on a purchase, version 1.4.0 has a Not sure yet option that asks again later. Skip the purchase and the money counts as a Diff. The free plan logs without limits, and there is no bank connection, so every number is one you chose to enter.

Keep the Diff is on the App Store and Google Play, and there are downloads for Mac, Windows and Linux on the download section of the home page. You can also try it in your browser first. Premium pricing is on the Premium page.

What if you break your own rule?

Both challenges have days when a rule bends. A low buy challenge expects it, and a no buy challenge feels it more. Either way, the useful response is to log what happened and keep going. The money you already kept stays kept. What to do when you buy something anyway covers this in more detail.

Low buy vs no buy: which challenge fits you