Synastry · Free calculator
House overlays calculator: whose planets live in whose houses
Enter two birth charts. See each person's planets in the other's houses, both directions, in Placidus or Whole Sign, with every cusp call flagged.
Photo: Clay Banks / Unsplash
At a glance
Enter two birth dates, times and places. The calculator places all ten of each person's planets in the other's houses and tells you who, by the house-person rule, feels it more.
- Directions
- Both, side by sideyour planets in theirs, and theirs in yours
- House systems
- Placidus or Whole Signuse one for both charts
- Cusp warning
- Within 2°13.5% of overlays land there
- 15-minute time error
- 12.6% change housein a test of 20,000 pairs
- Price
- Free, no accountno sign-up needed
Start the calculatorOr load two sample charts to see it work.
How it works
Two charts, ten planets each, twelve rooms to land in
Try this today
- No birth details yet? Load the two sample charts first and flip between directions.
- Ask your partner for their birth time before the date of birth. It is the bit people never remember.
It starts the way a first date does: you, them, and a lot of questions. The calculator asks just three per person.
For each person it computes a full birth chart: the ten planets from the Sun to Pluto, and the twelve house cusps for that birth time and place. Then it does the synastry step, which is simple geometry. Each of your planets is a point on the zodiac. Each of their houses is an arc of the zodiac. The calculator checks which arc each point falls inside. Then it does the same the other way round.
What comes back is two lists of ten, and they almost never mirror each other. Each line gives the planet, its exact position, the house it lands in, and a short reading. Every house links to its own page in the overlay library, so you can go deep on the one that made you gasp.
It also adds a "who feels it more" tally. The house person is the one who feels an overlay, so the tool counts how many of each person's five personal planets (Sun, Moon, Mercury, Venus, Mars) land in the other's 1st, 5th, 7th or 8th house: self, romance, partnership and intimacy. More hits means more of the other person landing in the intimate rooms of your life.
Reading the results
Read your overlays in four passes
Try this today
- Write down your three loudest overlays in each direction. Which three surprised you?
- Pick the overlay you feel most and open its page. Does the house person's side match your experience?
A list of twenty overlays is a lot. Here is the order astrologers tend to read them in.
- The loud ones. Rows shaded in the table are personal planets in angular houses (1st, 4th, 7th, 10th). Read those first: they are the overlays you notice in everyday life.
- The edges. A cusp note means the planet is within 2° of a house line. Read both houses. Many astrologers treat a planet just before a cusp as already working in the next house.
- The mirrors. Flip the direction. If both of you put planets in each other's 5th, or one person's 7th is busy and the other's is empty, that asymmetry is the story.
- The background. Uranus, Neptune and Pluto move slowly, so their house in your chart is shared with most people your partner's age. Read them last.
One more habit: switch to Whole Sign and back. An overlay that holds its house in both systems is a sturdier read than one that hops.
The birth time
The 15-minute test: why birth times matter so much
Try this today
- Re-run the calculator with the uncertain time 15 minutes earlier and later. Overlays that don't move are safe to read.
- If a time is a guess, say so out loud when you share the result.
Planets move slowly against the zodiac. The Sun covers about a degree a day. House cusps are different: they ride the turning Earth and sweep through the whole zodiac in a day.
On average the Ascendant moves about one degree every 4 minutes, but not evenly. At London's latitude it ranges from 1.7 to 5.7 minutes per degree through the day; at New York, 2.3 to 5.1. Some rising signs fly past.
So we ran a test. In 20,000 random pairs of births, we nudged the house person's birth time by 15 minutes and recomputed. 12.6% of overlays changed house. With a one-hour nudge, 50.1% did.
The practical lesson: the house person's time is the one that matters. If one of you has a certificate time and the other has "sometime after lunch," trust the overlays into the first person's chart more than the ones into the second.
House systems
Placidus or Whole Sign: pick one and stick with it
Try this today
- Toggle the system and note which overlays hold steady. Those are your most reliable reads.
- If you read your own chart in Whole Sign, read synastry in Whole Sign too.
Placidus is the most popular house system in modern Western astrology and the calculator's default. It divides the sky by time: how long each degree takes to rise and culminate. That makes houses unequal, especially far from the equator. At New York's latitude a Placidus 1st house can be anywhere from 19.5° to 48.1° wide.
Whole Sign is the oldest house system on record, used in Hellenistic astrology and still common in Indian astrology. The sign on the Ascendant is the whole 1st house, the next sign the 2nd, and so on: every house exactly 30°.
The two often disagree about overlays. In our sample, 53.9% of overlays landed in a different house under each system. That is not a glitch; they are asking slightly different questions. Pick the one you use for your own chart and use it for both people.
No birth time?
What still works when one time is missing
If you tick "I don't know the birth time," the calculator computes that chart for noon and stops pretending to know its houses. Overlays into that person's chart use solar houses: their Sun's sign becomes the 1st house, the next sign the 2nd, and so on. Some astrologers use this as a rough sketch. We label it, and so should you.
Overlays from that person into a partner with a known time still work, with one catch: the Moon. It moves about 13° a day, so a noon Moon can be well off. Read their Moon's overlay as a range, not a point.
Aspects between the two charts don't need houses at all. If the houses are a mystery, the synastry aspects guide is the better place to start.
The calculator
Find your house overlays
Add person 1, then person 2. Names are optional. The results show both directions; switch house systems or flip the view with one tap. Each house links to its own overlay page.
Person 1
Not added yet
Person 2
Not added yet
Person 1: you, or whoever goes first
No birth details to hand?
More to read
Shorter reads. Each opens in place.
Privacy
No account, no saved charts
The calculator sends each person's date, time and place to our chart engine, then shows the result in your browser. You don't sign in and nothing is saved to an account. Please only enter someone's details if they'd be happy for you to.
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The sample charts
Who are Sample A and Sample B?
Nobody. They are invented birth data, computed with the same method as the rest of this page: Sample A on 1996-04-21 07:40 in New York, USA, Sample B on 1994-11-03 09:30 in London, UK. They exist so you can see the tool work before typing anyone's details.
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Honest note
What a calculator can't tell you
It can tell you exactly where planets land. It cannot tell you whether a relationship will work: a 2020 study of Swedish register data tested zodiac-sign compatibility rules and found no consistent link with marriage or divorce (Helgertz & Scott). Read the overlays as a language for how you land in each other's lives.
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The sample charts, worked
Sample A (1996-04-21 07:40, New York, USA) and Sample B (1994-11-03 09:30, London, UK): invented birth data, computed with JPL DE442 planets and Swiss Ephemeris Placidus cusps.
| Planet | Position | Placidus house | Whole Sign house | Near a cusp |
|---|---|---|---|---|
| Sun | 1°38′ Taurus | 4th | 6th | yes |
| Moon | 13°22′ Gemini | 7th | 7th | |
| Mercury | 21°34′ Taurus | 6th | 6th | yes |
| Venus | 15°34′ Gemini | 7th | 7th | |
| Mars | 21°28′ Aries | 4th | 5th | |
| Jupiter | 17°23′ Capricorn | 2nd | 2nd | |
| Saturn | 1°39′ Aries | 3rd | 5th | |
| Uranus | 4°27′ Aquarius | 2nd | 3rd | |
| Neptune | 27°44′ Capricorn | 2nd | 2nd | |
| Pluto | 2°32′ Sagittarius | 12th | 1st |
| Planet | Position | Placidus house | Whole Sign house | Near a cusp |
|---|---|---|---|---|
| Sun | 10°43′ Scorpio | 6th | 6th | |
| Moon | 8°18′ Scorpio | 6th | 6th | |
| Mercury | 22°22′ Libra | 6th | 5th | |
| Venus | 10°02′ Scorpio | 6th | 6th | |
| Mars | 15°33′ Leo | 4th | 3rd | |
| Jupiter | 22°03′ Scorpio | 6th | 6th | |
| Saturn | 5°42′ Pisces | 10th | 10th | yes |
| Uranus | 22°49′ Capricorn | 9th | 8th | |
| Neptune | 20°51′ Capricorn | 9th | 8th | |
| Pluto | 27°17′ Scorpio | 6th | 6th |
| Latitude | Fastest | Slowest | Average |
|---|---|---|---|
| Equator (0°) | 3.7 min | 4.3 min | 4 min |
| New York (40.7°N) | 2.3 min | 5.1 min | 4 min |
| London (51.5°N) | 1.7 min | 5.7 min | 4 min |
| House | Area of life | Share |
|---|---|---|
| 1st | self and first impressions | 8.7% |
| 2nd | money and self-worth | 8.6% |
| 3rd | talk and everyday life | 8.6% |
| 4th | home and family | 8.4% |
| 5th | romance and play | 8.4% |
| 6th | routines and health | 8.6% |
| 7th | partnership | 8.1% |
| 8th | intimacy and trust | 8.1% |
| 9th | travel and beliefs | 8.1% |
| 10th | career and reputation | 8.0% |
| 11th | friends and the future | 8.2% |
| 12th | the private inner world | 8.2% |
All times are UTC. In the Americas the local date can be a day earlier; in Asia and Australia a day later.
Quick answers
Is this synastry house overlay calculator free?
Yes, free and with no account. The birth details are sent to our chart engine to compute the two charts, and the results are shown in your browser. Nothing is saved to an account.
How does the house overlays calculator work?
It computes both birth charts (planet positions and house cusps), then places each person's ten planets in the other person's houses. You get two lists, one per direction, plus a note for any planet within 2° of a cusp and a tally of who feels it more.
Who feels it more in synastry, according to the calculator?
The calculator counts each person's share of the other's personal planets (Sun, Moon, Mercury, Venus, Mars) landing in their 1st, 5th, 7th or 8th house. The person with more is, by the house-person convention, the one likely to feel the other more. It is a rule of thumb from the tradition, shown with its working.
Can I calculate house overlays without a birth time?
Only roughly. Without a time we can't know that person's houses, so the calculator uses solar houses (their Sun sign as the 1st house) and labels them. Their planets can still be placed in their partner's real houses, apart from the Moon, which can move about 13° in a day.
Why do my overlays change between Placidus and Whole Sign?
Placidus houses are unequal and start at the exact degree of each cusp; Whole Sign houses are whole signs, 30° each. In our test of 20,000 random pairs, 53.9% of overlays changed house between the two. Use the same system for both charts.
How accurate does the birth time need to be?
As close as you can get. On average a chart's Ascendant moves about one degree every 4 minutes, and in our test a 15-minute error changed the house of 12.6% of overlays. A birth certificate time beats a remembered one.
What do the sample charts show?
They are two charts computed from invented birth data, not real people, so you can see the calculator work before entering anyone's details. In the samples, Sample A's Moon and Venus land in Sample B's 7th house.
