⊗ Free Arabic Parts & Lots Calculator
Umbriel computes the Part of Fortune, the Part of Spirit and the rest of the traditional lots — including the day/night formula reversal that most calculators quietly skip. Free, in your browser, no account.
- What you'll needBirth date, time and place
- What you getEvery traditional lot with its formula shown, correctly reversed for a night birth, plus its sign, house and aspects
- CostFree — no account required
Runs in your browser. Nothing to install, nothing to set up.
What it actually is
The lots — often called Arabic parts, though they predate Arabic astrology — are calculated points rather than bodies. Each is derived by measuring the distance between two placements and projecting it from a third, usually the Ascendant. The Part of Fortune, the best known, is the Ascendant plus the Moon minus the Sun.
⚠️ And for a night birth, that formula reverses: Ascendant plus the Sun minus the Moon. This is not a minor variant. It moves the Part of Fortune to a completely different degree, often a different sign and house, and it is the single most common error in lot calculation — plenty of software applies the day formula to everyone.
Umbriel checks whether the Sun is above or below the horizon and applies the correct formula, and it shows you the formula it used rather than presenting a number you have to trust.
The lots go far beyond Fortune. There are lots for spirit, eros, necessity, courage, victory and more, each with its own formula, and the traditional material treats them as specific rather than general.
How Umbriel computes it
Sect is determined from the Sun's actual altitude relative to the horizon at your birth, not from clock time, and the day or night formula is selected from that. Each lot is then computed by the arc-and-project method rather than by adding raw longitudes, so a lot whose components straddle 0° Aries lands in the right place. The formula used is printed alongside the result — which is the point, because the day/night reversal is the most commonly mishandled thing in this whole area and a bare number gives you no way to tell whether it was applied.
What's in your result
- The Part of FortuneWith the day or night formula applied correctly for your birth.
- The formula, written outSo you can check the arithmetic rather than take the result on faith.
- The Part of Spirit and the restThe full set of traditional lots, not just the famous one.
- Sign, house and aspectsEach lot placed in your chart and aspected like any other point.
- Day or night, stated plainlyWhether your birth was diurnal or nocturnal, since everything here turns on it.
Common questions
What is the Part of Fortune?
A calculated point, not a body: the Ascendant plus the Moon minus the Sun for a day birth. It is the best known of the traditional lots and is read as a point of ease and material wellbeing.
Does the Part of Fortune formula change at night?
Yes, and this catches a lot of software out. For a night birth the formula reverses to Ascendant plus Sun minus Moon, which puts the point somewhere completely different. Umbriel applies the correct one and shows you which.
How do I know if my birth was day or night?
By whether the Sun was above or below the horizon — not by the clock. A birth at 5am in June is usually a day birth; the same clock time in December is usually a night one. Umbriel works it out from your chart.
Do I need a birth time for the lots?
Yes. Almost every lot is projected from the Ascendant, and the day/night distinction depends on the Sun's position relative to the horizon. Both need a birth time.
Is the Arabic parts calculator free?
Yes — the full set of traditional lots with their formulas shown, and no account.
Go deeper
Each of these is a free tool in its own right.
Umbriel offers every system here as a set of prompts to think with, never as a statement of fact about who you are. Take what's useful, leave the rest.