When calculating a chart, you can choose from many different house systems. Of course, all astrologers are convinced that their preferred method is superior to the others.
I use the Placidus system. It's the first one I was introduced to, so I decided to stick with it. Frankly, that's how most astrologers pick a house system: they pick up a book or take a class and then stick with the first one they learned.
How do you know which one to pick or which is best? It all comes down to trial and error. I recommend that you test-drive each system and see what makes the most sense to you. Feel free to ignore people who say that their house is better (or bigger) than yours. We're not trying to keep up with the astrological Joneses here.
Without further ado, here are a few good choices to explore:
Placidus: In modern Western astrology, this is the most widely used house system. In the Placidus system, the houses may be larger or smaller than 30 degrees, which creates what's known as intercepted houses. If you live far from the equator (both south or north), those houses can be really uneven.
Koch: Koch is similar to Placidus, but the method of calculating is slightly different. Like Placidus, this chart casting method also creates houses that can be larger or smaller than 30 degrees; hence it also has intercepted houses. (I once got into an argument with a guy who claimed this was the “only accurate” method. Like I said, astrologers get defensive over their chosen systems!)
Whole Sign: I've met quite a few folks who love the Whole Sign method. It's one of the oldest house systems. Here, the houses are exactly 30 degrees each. The first house starts at 0 degrees of the zodiac sign, and the rest of the houses also begin with 0 degrees. Everything is nice and neat.
Equal House: This house system is similar to Whole House, but the degree of the rising sign determines the rest of the houses. In other words, if your Ascendant began at 20 degrees Gemini, the next house would be 20 degrees Cancer and so on.
These are only a few of the house systems to choose from, but they are the most popular. There are also Natural Houses, Regiomontanus, Campanus, and more. You can experiment by changing the house calculation methods on your astrology software. Again, test them all out. Which one do you like? What feels right? That's what matters.
As I mentioned, if you're using the Placidus or Koch house system, you may notice that some of the houses might seem more massive than the others. When this happens, it might appear that some signs are missing on the house cusps. Breathe easy: they are not! Instead, you'll notice that those signs are smack dab in the middle of the house.
For example, I have Sagittarius on the third house cusp, but Aquarius is on my fourth house cusp. Capricorn, therefore, is intercepted between these two and hangs out in the third house. It's kind of like a hidden door. If a sign is intercepted, the opposite sign will be as well. Using myself as the example again, Cancer is also intercepted.
An intercepted sign can indicate a blockage or a hidden part of yourself that is not obvious on the surface. Some astrologers believe that intercepted signs suggest you didn't get the support you needed in your childhood to develop the abilities of the intercepted signs. This means the energy lies dormant until one day it comes rushing to the surface—and not always in a good way. Think of it like shaking a soda can: you take off the cap, and it sprays all over the place!
I have seen interceptions manifest differently. The early environment still plays a role in that it created conditions for the energy of the intercepted sign to flourish in secret. It's not outwardly expressed until later in life.
Using myself as an example again, I have Sagittarius on my third house cusp, which makes sense to most people when they meet me. I'm philosophical and jovial. I like to talk about spiritual matters and world events as well as my latest travels. But I'm also extremely practical, orderly, and methodical in my thinking—and highly ambitious. Just like a Capricorn! That side of me came out later in life when I got deadly serious about my business. Even though I don't have an MBA, my brain is hardwired for CEO stuff.
A planet is considered intercepted when it's in the intercepted sign. For example, if Scorpio is intercepted on your seventh house and you have Venus in Scorpio, this interception might indicate that you have a robust possessive streak that you repress. It may get triggered from time to time, but for the most part, it's dormant.
Once again, using myself here: Gemini on the ninth shows that I like to study and travel. It indicates a curiosity about the world. All true. But I have Venus intercepted in Cancer sitting in my ninth house—this shows a love of home. Although I travel extensively, I'm a homebody at heart. Nothing makes me happier than hunkering down with a glass of wine, a home-cooked meal, and Game of Throne reruns.
Frank Sinatra had Capricorn intercepted in the third house, just like me. He also had Venus intercepted, but his was in Capricorn. See the arrows in the image here. How might that intercepted Venus in Capricorn show up in his life?
If you do not want to deal with interceptions, then you may want to use the Equal or Whole House systems instead. It's all good!