The view of this put forth above is quite wrong. Your approach to calculating the "returns" from law school is incorrect, and your estimates are also dangerously optimistic. The proper comparison is this:
(1) You can either stay at your $45k job or go to law school for three years.
(2) At the end of law school, assume you get a job paying $65k.
(3) Salary at both jobs will increase at 4% per year, and your discount rate (inflation) is about the same.
After the three years of work, you have earned $94,500 in net income after taxes. After three years in law school you have earned zero income and taken on a bunch of loans. Then you have an (assumed) higher starting salary with your JD, compared to your prior salary of $45k which has just increased by our assumed 0.04 per year in the past three years. The problem is that after law school you have $150k in debt, which reduces your net income by $1,100 per month.* As a result, your post-JD net, take-home income does not pass up your expected income from your prior job until at least eight years out.
So right away you're worse off, and even over the long term it's a total net present value loss of $32,000. Plus you've signed on to 30 years of working as a lawyer in order to realize that loss. Still, if you really want to be a lawyer, then maybe that is worth $32k to you. It gets worse though. Change your expected starting salary to a more plausible $55k** as reflected by the lower mode of the salary distribution of new attorneys
, then up your debt to a more likely $180k to cover total cost of attendance, and you've got a net loss of $13k per year take home income the day you graduate from law school, with a quarter million dollar financial disaster on your hands over the long term (so much for buying a house . . . or retiring . . . and God help if you plan to have kids). This is much closer to the ACTUAL outcome for about 8 in 10 people who right now are considering doing exactly what you're suggesting.
(*) Income during law school will at best only reduce your loan balance, and you will be lucky to come out with ONLY $150k if you're starting law school today. Total cost of attendance is busting $60k per year at most schools, and that's assuming you are single, can live cheap as hell, and will have some sort of work to cover your summer expenses. You might come out only owing $150k if you already have $30k saved, or have a working spouse, or get Big Law your second summer (and this entire analysis obviously assumes that you will not). Also, a realistic interest rate is closer to 8%, especially with fees figured in, but even 7% only makes things marginally less awful.
(**) Even that is shaky, and probably a generous assumption in the current market. Many new grads, even three years from now, are going to be looking at starting salaries after the JD of around $45k. And this is assuming they get jobs at all -- something like 1/4 to 1/2 of new lawyers will wind up unemployed and unemployable each year, and this figure shows no sign of improving any time soon. Obviously the people taking on six figures of debt to make the same gross salary they gave up to attend law school are going to come out even worse than the worst case above.