In the last couple of weeks, we explored the very first things you should be doing to prepare yourself for applying to law school this fall. (Here are Step 1 and Step 2, in case you missed them.)

By now, you should have created your LSAC account and registered for the October LSAT. (If you already took the June LSAT last week, gold star for you!) You should also be seeking out a great LSAT class or tutor. Not just good, but great.

Why does the LSAT matter so much? And why is a great LSAT course worth the investment? Because the single biggest factor predicting your law school admissions outcomes will be a combination of your undergraduate record and your LSAT score. GPA + LSAT = Huge.

You'll hear some people tell you that you can "write your way" into law school or "write your way" around bad numbers, but that's rare. You might also hear some admissions officers tell you that the LSAT is only one factor among many (technically true, but they are not all weighted equally), or that it's only a validating tool. Fiddlesticks. What actually happens is that the non-numbers parts of your application come into play if and when your numbers, in combination, put you in the ballpark. That's when your written materials and other soft factors really count the most, and when they can make the difference between an offer and a ding letter.

By the time you apply this fall, your undergraduate record is whatever it is, so let's treat that as a constant at this point. But your LSAT... your LSAT is still a variable, and a big one at that. That's a great opportunity. So buckle down and focus your energies on the LSAT between now and early October, if you haven't already taken it.

How do you get a rough sense of your odds? The best place to gauge your acceptance odds based on your numbers is the LSAT/GPA calculator on the LSAC website (look for a box labeled "LSAT/GPA Search," currently on the upper left part of that linked page). The calculator will give you an idea of what LSAT score you'll need in order to be competitive at various schools. That information can guide you both as you decide which schools to research further, and also as you embark on your LSAT preparation and start taking practice tests.

Once you're on that calculator page, plug in your undergraduate GPA on a 4.0 scale, plug in any real — or hypothetical — LSAT score, and see how last year's applicants fared at different schools with those same numbers. (You may find the information easier to digest if you then sort the results by "Llkelihood" rather than "Alphabetical.")

I like to see an applicant exceeding 40% odds to be in the running, but that's just a rough estimate, and certainly your list can include some reach schools. (Reasonable reach schools, and no more than one parallel-world, never-gonna-happen-but-I-just-want-to-see reach school, unless you generously want to donate your application fees out of the goodness of your heart.)

The LSAC site isn't the only place where you can run your numbers. There are several websites out there that help you predict your odds, but LSAC is the only website that has a complete data set for applicants to different schools. (LSAC captures the numbers and admissions results for every single applicant who applies to an LSAC school, so they have a trove of information.) Not all schools participate in the calculator — there are still some hold-outs — but most schools do.

There are trade-offs, of course. The LSAC calculator does not break out the results based on other important factors like ethnicity, or whether a person applied in November vs. February. Those things can make a big difference. On the other hand, non-LSAC predictor websites rely on self-reported information by self-selected applicants, so they have some limitations as well. You can and should avail yourself of those other sites, but make sure to use them in combination with the LSAC calculator.

A note on timeline: Because the LSAT matters so much to your admissions outcomes, you won't be able to put together an appropriate list of schools until you have your score. One big reason why waiting until October to take the LSAT is not ideal is because you won't have your score until late October. I generally recommend that people submit their completed applications on or around November 1st, so if you wait until you have your October score before starting work on your applications, you're not leaving yourself much time to get the job done, and to do it well. You'll need to start working ahead of time on some parts of your application that you'll be submitting no matter where you end up applying, and then reserve the month of October (post-LSAT) to work on the bits that are school-specific, and to customize your general materials for your various schools. And if you're an early bird who is reading up before applying next year, you can give yourself plenty of time to prepare for the June test (or even an earlier one).

Former Dean of Admissions at the University of Chicago Law School and a recovering lawyer, Anna Ivey founded Ivey Consulting to help college, law school, and MBA applicants navigate the admissions process. Read more admissions tips in The Ivey Guide to Law School Admissions, recently updated as an e-book. Follow Anna on Twitter (@annaivey), or come introduce yourself and join the conversation on Facebook.