The question is the gap, not the calendar
There is no universally correct start date. What matters is the distance between the score you get cold and the score you need, and the only way to know that distance is to take a full timed official practice test before you plan anything.
Your target comes from your college list. Each school publishes the 25th and 75th percentile SAT scores of its enrolled students in section C9 of its Common Data Set. Aim at the middle of that range for your list, not at a number someone called good.
Subtract. That difference is what your study plan has to close, and it decides your timeline.
Solve for x: x² = 36
Rough lead times by gap
A gap of about 100 points is usually an execution problem. Careless errors, blanks, and pacing account for most of it, and six to eight weeks of consistent work is normally enough. That is four or five sessions a week of 45 to 60 minutes, plus a full practice test every other weekend.
A gap of about 200 points mixes execution and content. Plan on roughly three months, with the first half spent domain by domain and the second half on mixed practice and full tests.
A gap of 300 points or more is a content problem. Plan on six months or more, and accept that some of the closing will come from coursework as you finish Algebra 2 rather than from SAT practice alone. These ranges are rules of thumb based on how the material is structured. They are not published figures and your own rate will vary.
Work backward from the date
Pick your target sitting first. For the current cycle the dates are October 3, November 7, and December 5 of 2026, and March 6, May 1, and June 5 of 2027, with registration deadlines about two weeks before each.
Then count backward by the lead time your gap implies, and add two weeks of slack for the weeks that will not go as planned. If the start date lands in the past, either pick a later sitting or narrow the plan to the highest value fixes and accept a smaller gain.
Leave room for a retake. Most students improve on the second sitting, so the first date should not be the last one available before your earliest application deadline.
Why starting a year out backfires
A twelve month plan sounds diligent and usually collapses. Motivation for a deadline a year away is hard to hold, and material learned in September is gone by June unless you keep reviewing it, which doubles the work.
There is also the content problem. Starting before you have finished the math your school will teach you anyway means grinding through material that will be handed to you in class for free.
A focused eight to twelve weeks beats a distracted year, and it leaves your attention available for grades, which most colleges weight more heavily than the test.
If your test is soon
Inside three weeks, stop trying to learn new content. Take two or three full practice tests and spend more time reviewing them than taking them. Drill only the content gaps that showed up more than once.
Fix pacing instead. About 71 seconds per Reading and Writing question and about 95 seconds per Math question, with a hard rule that you guess, flag, and move on at twice that. With one minute left in a module, fill in every blank, since there is no penalty for a wrong answer.
In the last two days, no full tests. Short warm up sets, your mistake list, and the logistics: Bluebook installed, exam downloaded, device charged, ID matching your registration.