So, you've recorded and mixed your own material.  Now your at the mastering stage.  Are you thinking of mastering your project yourself?  Before you do, ask yourself this question.  What is my definition of mastering?  If you answered, I simply
want to make it as loud as commercial releases, then your understanding of what mastering is needs to be expanded.  The definition of mastering is: To enhance the presentation of a mix so it sounds its best on the widest variety of playback systems.
Unless you have the experience and the proper tools to achieve that result, you may not really be mastering.  You could just be changing the mix.  Unless requested by the client, mastering shouldn't change the mix.  It should enhance the presentation.

Here are additional questions you should ask before you begin to master your project yourself.

1. Did my favorite music equipment dealer tell me I could master my own projects if I purchased Brand X audio software?
2. If I master my own project, what do I expect to accomplish that's different from what I've already achieved in the mix?
3. Am I going to master in the same room I mixed in, using the same monitors, the same gear, and of course, the same ears?
4. If my answer to #3 is yes, will I really be able to determine what needs to be improved?
5. Will I be making adjustments during the mastering stage that should really be made by going back to the mix?
6. Can I burn a Red Book CDR that will exceed, or at least meet the requirements of CD replicators?
7. Can I embed CD Text and ISRC Codes onto my CD?

Seriously think about your answers to these questions before you proceed, especially number 6.  Many artists have become confused while facing the challenge of mastering their own projects.  Unfortunately, far too many do it yourself artists think that mastering simply means making it louder.  Just making it louder isn't mastering at all.  It's simply making it louder.  Anyone can slap a brick wall limiter on the output buss and raise the level 6 to 10 dB.  However, that's not mastering.  It's messtering.

You can search high and low on the Billboard Charts, and you'll never find a song that was recorded, mixed, and mastered, by the same person in the same room, using the same gear.  When a song hits the charts, you can be sure it was mastered in a tuned room with proper monitors, specialized gear, and most importantly, an experienced engineer with a fresh set of ears.

Mastering is the quality control phase of a project.  It should never be taken for granted, especially if the recording and mixing took place in a home studio.

Equipment dealers are only too happy to confuse the do it yourself mastering issue.  After all, it's their job is to sell products. They'll be more than happy to sell you a computer and convince you to buy the software necessary to guarantee professional results.  However, what they can't sell you is the experience it takes to enhance the presentation of a mix so it sounds its best on the widest variety of playback systems.  Mastering tools are just that... tools.  Just because you have an auto mechanics tool chest filled with all the latest tools, doesn't mean you can repair a car.  Education and experience are also necessary.

Having the right gear is great.  However, it's the mastering engineer (not the gear) who listens objectively and makes the right decisions.  The talent to make the right decisions cannot be found in hardware, software, or plugin presets.

If your project is just for fun, then master it yourself and have fun.  However, if you're serious and plan to market your music,
I strongly recommend having your project mastered by an experienced mastering engineer.  Remember, mastering shouldn't change your mix.  It should preserve your musical vision while enhancing the presentation.