What's up with online birth charts being off by many degrees?

I've explored several websites that offer birth charts and noticed that their calculations differ in some cases by as much as 15 degrees. This means that they assign different ascendants and houses, which significantly alters the information on the chart.

Why are these websites using such different calculations for birth charts?
How do I know which websites to trust?

astro.com is probably the best site to calculate your ascendant on

rahu

astro.com provides reliable charts.

Their free service includes the casting of many types of charts, not limited to natal figures.

Its why I never use the data on charts done on the internet, or the charts here(and of course why if the data is not provided, I ignore the post). I use two purchased programs:

1. Haloran's Astroldeluxe

2. Astrolabe's Solar Fire.

If there is a difference between them is in minutes, its becuase John Halloran is a perfectionist to the anal extreme, so his calculations are probably the correct ones.

In astro.com's defense, they are never more than 2 minutes off of John Haloran's programming.

I always use astro.com for erecting charts (except those that I erect or modify by hand)

I've used astrolog for many years and Walter Pullen (who created astrolog) has collaborated with Robert Hand and the ephemeris for astro.com. The "extended chart" selection has a section for astrolog although it doesn't really work as well as the actual program does natively on a home computer. I love the native program because you can cycle through in real time on many different charts which other programs can't, as well as switching 1000 different options on the fly.