About Keep the Diff
What it is
Keep the Diff is a money saving app built on one subtraction. You record what you were ready to spend and what you actually spent, and the difference is kept as a running total of money you decided not to part with.
It is not a budget. It never tells you what you are allowed to spend, it does not connect to a bank, and it has no red numbers, because a total of money kept has no way to express disapproval. The lowest a week can read is zero.
Who makes it
Keep the Diff is made by Lee, trading as Little Bird Trading LLC. It is a one person operation. The same person writes the code, the copy on this page, and the replies to the support address, which is worth knowing before you send one.
The longer version of why it exists is on the home page, in the founder's own words. The short version is that every budgeting app tried first started by asking for a bank connection and then spent the rest of its life reporting what had already gone wrong. None of them ever recorded the decisions that left money in the account in the first place.
Why decisions rather than transactions
Every personal finance tool is built on transactions, so the only events it can see are the times money left. A decision not to spend produces no transaction at all: no line in a feed, nothing to categorize, nothing to import.
That makes an entire category of software blind to the behavior it is supposed to encourage. Keep the Diff records the decision instead, which is the only design choice in it that really matters. Everything else follows from that one.
What it costs
Logging decisions is free and always will be, along with this week's total, your recent history, the weekly recap and your choice of currency. Premium adds full history with CSV export, categories, goals, widgets, the watch app and App Lock. One subscription covers every device you use.
Prices and what is in each tier are on the pricing page.
What it does with your data
There is no account and no sign-in. The app does not connect to a bank, and the numbers you type stay on your device. The privacy policy is short enough to read in full, which is deliberate.
Where it runs
iPhone, iPad, Mac, Apple Watch, Windows, Android and Wear OS. There is also a version that runs in this browser with nothing to install, a sheet you can print, and a calculator.
The other things Little Bird Trading makes
Keep the Diff is one of several small, single purpose apps built by the same person: Reveal the Dream, a vision board; MyLinedChart, charting and export for traders; The Long View, for quitting smoking; and Still Dock, which keeps the Mac Dock where you put it. They share nothing but an author and a preference for doing one thing without asking for an account.
Getting in touch
The support page has the common questions and a contact form, and hello@littlebirdtrading.com reaches a person rather than a queue. If something is broken, saying which device and which version gets you a useful answer considerably faster.