Duet: side by side
Tools that put two things next to each other and show you exactly what is the same and what has changed: lists, files, documents and data.
About Dueter
Small tools for the dates and details that matter
Dueter builds free, fast web tools for working out deadlines and comparing things side by side. No sign-up, no clutter, and the maths happens right in your browser.
The name
Two ideas in one word
Dueter is a blend of duet and due. Every tool we make does one of those two jobs well.
Due: on time
Tools that turn payment terms, working days and deadlines into a clear date, so you always know when something is due.
What we stand for
Built to be trusted, not just used
Four rules every Dueter tool has to pass before it goes live.
Accurate
Every calculation is checked against worked examples and the rules behind it, including the awkward month ends.
Private
Our tools do their maths in your browser, and we never store or log the numbers you enter.
Fast
Pages load in a blink and results update as you type. No spinners, pop-ups or waiting on a server.
Free
The core tools are free to use, with no account and no limit on how many times you use them.
How we build
From a real question to a finished tool
1
Find the question
We start from things people search for every day, like "when is a Net 30 invoice due?"
2
Get the rules right
We map out the rules, edge cases and the exceptions people trip over.
3
Build it lean
One focused screen, instant results, and it still works with JavaScript turned off.
4
Explain it
Each tool comes with a plain-language guide, worked examples and answers to common questions.
0sign-ups needed
100%runs in your browser
12payment term types covered
Freefor every core tool
Have an idea for a tool?
Tell us what you keep working out by hand. The best suggestions become the next Dueter tool.