About Keep the Diff
What Keep the Diff 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.
There is no budget. The app 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 the app
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 the app 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 the app records decisions
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 to categorize or import.
So an entire category of software is blind to the behavior it is supposed to encourage. Keep the Diff records the decision itself, and that is the only design choice in the app that really matters. Everything else follows from that choice.
What the app costs
Logging decisions is free, along with this week's total, your recent history, your choice of currency and the weekly recap. 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 the app does with your data
No account is needed and signing in is optional. The app does not connect to a bank, and we never see the numbers you type. The privacy policy is short enough to read in full, which is deliberate.
Where the app runs
iPhone, iPad, Mac, Apple Watch, Windows, Linux and Android. There is also a version that runs in this browser with no 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; Still Dock, which keeps the Mac Dock where you put it; Copy Shelter, which backs a Mac and an iPhone up to storage you already own; and Prompt Petal, which keeps the AI instructions you use most one click away. 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 goes straight to a person. If something is broken, saying which device and which version gets you a useful answer considerably faster.