Search for a no spend challenge app and you get a page of them, plus a few tool pages from companies that also make one. They look different and they work almost identically. Before you install any of them, it is worth knowing which differences are real.

This is a buyer's guide rather than an argument. If you want the argument about why scoring matters at all, that is a separate post.

1. How it scores you

This is the one that decides everything else, and nearly every app answers it the same way: a streak. Consecutive days without a purchase, shown as a number or a calendar you fill in. Their own descriptions say so plainly. Build a streak. Watch it grow. Buy something and it resets.

The alternative is a running total of money. Instead of counting days you survived, it adds up what you decided not to spend. The difference sounds cosmetic and it is not: a streak can be destroyed and a total cannot.

When you are comparing apps, this is the first thing to find out, and it is usually visible in the screenshots. A big number with the word "days" under it is a streak. A big number with a currency symbol in front of it is a total.

2. What it does on a partial win

You were going to spend ninety dollars and you spent forty. Almost every no spend challenge app has no way to record that, because its unit is a day and a day is either clean or it is not. Forty dollars spent means the day is spent, and the fifty you saved disappears.

For most people the partial decisions outnumber the outright refusals. The cheaper option, the smaller size, the store brand, the repair instead of the replacement. An app that cannot express any of it is not measuring most of what you did.

Ask of any app: can I record that I spent less, rather than only that I spent nothing?

3. What happens when you stop for a week

Life interrupts. You go on holiday, you get ill, you forget. What does the app look like when you come back?

Under a streak, it looks like zero, and it looks the same as it did before you ever started. Everything you did in the first three weeks is gone from the screen. That is the moment most people delete the app, and it is a reasonable reaction rather than a failure of character.

Under a total, it looks like whatever it looked like when you stopped. Coming back means adding to a number that is still there.

4. Whether it wants your bank

Some spending trackers ask you to connect an account so they can read your transactions. For a no spend challenge this is close to useless, because the thing you are tracking is a purchase that did not happen, and a purchase that did not happen produces no transaction to read. There is nothing in the feed to find.

So an app in this category asking for bank access is asking for something it cannot use for the job you downloaded it for. That is worth noticing.

The related question is what happens to what you type in. Look for whether there is an account to create, whether the data sits on the device or on somebody's machine, and whether the privacy policy is short enough to read.

5. What it costs, and what the free tier really includes

Most of these apps are free to install and charge for something. What matters is which side of the line the core loop sits on. If logging a decision is behind the paywall, the free version is a demo. If logging is free and the extras are history, export, categories and widgets, you can use it for a month before deciding anything.

Check this in the store listing before installing, because it is much easier to read there than to discover on day nine.

A short checklist

Streak or total? If the headline number can go back to zero, know that before you start caring about it.
Can it record spending less? Not just spending nothing.
What does a gap look like? Open the app, skip three days, look again.
Does it need an account or a bank connection? For this task, neither is necessary.
Is logging free? The core loop should not be the paid feature.

Where Keep the Diff lands on each

It scores a money total rather than a streak, so there is nothing that can reset. It records partial wins, because you enter what you were ready to spend and what you actually spent, and the difference is the entry. A gap in your logging leaves the total exactly where it was. It does not connect to a bank, there is no account to create, and what you log stays on your device. Logging is free, and always will be, along with this week's total, your recent history and the weekly recap.

That is one honest answer to the five questions above, and it is deliberately the answer this app was built to give. If you would rather check the reasoning first, there is a longer explanation of the approach, or you can try the scoring in your browser without installing anything.

No spend challenge apps compared: what to actually look for