Math, written like a note.
Type one calculation per line and Ilumi answers beside it, with variables, units, currencies and dates built in. Free and open source for macOS, Windows and Linux.
sum adds up the lines above it.Money in any currency
Add up a trip in euros and see it in dollars. Rates refresh every hour and still work offline, flagged when they may be outdated.
- flights = 2 * 480 EUR
- 960 EUR
- hotel = 6 * 95 EUR
- 570 EUR
- food = 6 * 40 EUR
- 240 EUR
- trip = flights + hotel + food
- 1,770 EUR
- trip in USD
- 2,017.08 USD
- trip / 2
- 885 EUR
Percentages the way you say them
Name a value once and reuse it. A 5% discount, 15% of the subtotal, plus 8%: Ilumi reads percentages the way you would say them.
- hours = 38
- 38
- rate = 85
- 85
- subtotal = hours * rate
- 3,230
- discount = 5%
- 0.05
- subtotal - discount
- 3,068.5
- tax = 15% of subtotal
- 484.5
For the work in your other window
CSS pixels and rems, hex and binary, bitwise operators, data sizes. The scratchpad that stays open next to your editor.
- 24 px in rem
- 1.5 rem
- 1.5 rem in px
- 24 px
- 0xF0 OR 0x0F
- 255
- 255 in hex
- 0xFF
- 0b1010 << 2
- 40
- 1.5 GB in MB
- 1,500 MB
Dates and time zones
Count the days to a deadline, turn them into hours, and check what time it is in Tokyo or New York. More than 400 time zones.
- deadline = today + 3 weeks
- Sun, Oct 18, 2026
- deadline - today in hours
- 504 hr
- now in Tokyo
- Mon, Sep 28, 2026, 2:12 AM GMT+9
- now in New_York
- Sun, Sep 27, 2026, 1:12 PM EDT
The rest of the toolkit
Small things that make it the calculator you keep open.
Always one shortcut away
Show or hide Ilumi from any app. Keep it on top of other windows if you like.
Cmd/CtrlAltSpace
Refer to the lines above
sum, avg, prev and count work on the results above, so totals never need retyping.
- 10 + 20
- 30
- prev * 2
- 60
200+ units
Length, weight, volume, area, temperature, time, data and CSS units, converted with in.
- 100 °C in °F
- 212 °F
Functions and constants
Square roots, rounding, trigonometry and logarithms, with pi and e ready to use.
- round(10 / 3, 2)
- 3.33
Your number format
Choose 1,234.56, 1.234,56 or 1 234,56, and how many decimal places to show.
Notes in tabs
One note per project or errand. Everything saves as you type.
Plugins
Add your own units, functions and constants with a small JavaScript file.
Share as an image
Copy a note as a picture, ready to paste into a chat or an email.
Questions
Is Ilumi free?
Yes. Ilumi is free and open source under the MIT license. Donations help, but nothing is locked behind them.
Which systems does it run on?
macOS (Apple Silicon and Intel), Windows (64-bit and ARM) and Linux (.deb and AppImage, for x64 and ARM).
macOS says Ilumi “cannot be opened”. What now?
Ilumi is not signed with an Apple Developer ID yet, so macOS blocks the first launch. Run xattr -cr /Applications/Ilumi.app in Terminal, or open System Settings → Privacy & Security and choose Open Anyway.
Does it need an internet connection?
No. Calculations run on your computer and notes are saved locally. The internet is used only to refresh exchange rates and check for updates; offline, Ilumi uses the last known rates and marks results that may be outdated.
Can I add my own units or functions?
Yes. Plugins are small JavaScript files that add units, functions and constants. The plugin guide on GitHub shows how.
Open a note. Start counting.
Ilumi is built in the open. Report a bug, suggest a feature or write a plugin.