When you make soup from scratch, you have plenty of details to worry about. You probably need to prepare many of the ingredients before tossing them into the soup pot. With so many tasks to complete to simply make soup, the last thing you need on your plate is another preparation detail. Fortunately, you can use a shortcut when adding pasta to soup. Instead of cooking it separately, you can add dry pasta to the soup and let it cook in the broth.
Make the soup as your recipe dictates. If at any point it tells you to boil or cook the pasta separately, ignore that part of the instructions, and simply continue making the soup.
Add the pasta to the soup five to 15 minutes before the soup is finished, according to the recipe. Stir well to distribute the pasta throughout the soup, then stir every one to two minutes while continuing to simmer the soup.
Check the pasta every few minutes by scooping out a single piece with a spoon. If you are using particularly small pasta, start checking it four to five minutes after adding it to the soup, then every few minutes thereafter. For larger pasta, start checking it five to seven minutes after adding it to the soup, then every few minutes thereafter. You can use the directions on the box or bag of pasta to give you a rough estimate of when the pasta you added will be done. Allow the piece of pasta to cool, then eat it. Pay attention to its texture, and remove the soup from the heat when the pasta reaches the doneness you desire.
Adding dry pasta directly to the soup will cause your finished soup to be cloudier than it would have been otherwise. In some recipes, this might not matter, but in others, you might decide that the convenience is not worth the extra cloudiness. Consider using some extra liquid when you begin your soup to make up for the liquid that the pasta will absorb as it cooks. If you do not add extra liquid, your final soup will be thicker than it would have been otherwise.