The honest answer is that the number is the wrong question. A student who takes four full-length tests and analyses each properly will finish ahead of one who takes twelve and reviews none. But since "it depends" is not much help, here is the reasoning that produces a number, and then the number.
A practice test is an instrument, not a workout
This is the whole argument. A full-length SAT tells you where you currently stand and, far more usefully, produces a fresh error profile. It does not teach you anything. The teaching happens in the days afterwards, when you work out why each wrong answer was wrong and change what you practise.
A student taking a test every Saturday is measuring weekly and studying never. The predictable result is a flat line across five tests, followed by the conclusion that they have plateaued. They have not plateaued; they have never started.
The rule: only test when the result could have changed
Take a full-length test when enough focused work has happened since the last one that the error profile could plausibly look different. In practice that is rarely less than two weeks, because closing even one skill gap takes that long when a student has six to ten hours a week alongside school.
Applied to the common preparation lengths, that produces roughly:
- 8 to 12 weeks: four or five full-length tests, about one every fortnight.
- 3 to 6 months: six to eight, every two to three weeks.
- 6 months or more: eight to ten, spaced further apart early and closer together in the final two months.
In every case, the last full-length test goes about a week before the exam. The final week is for reviewing your own error log and sleeping, not for generating data you no longer have time to act on.
Where the tests should come from
Start with College Board's free full-length practice tests. They are adaptive, official, and run in the same application as the real exam, so they measure the thing you actually want measured.
Two consequences follow. First, the official supply is finite, so do not burn through it in the first month — a student on a six-month plan should ration it. Second, non-adaptive paper practice tests are fine for drilling content but their totals should not be read as predicted scores, because they cannot reproduce the routing decision that sets your reachable range.
The review is the study session
Budget as long for the review as most students budget for the next test. The routine that works:
- Before reading any explanation, redo every question you got wrong, untimed. Note which you now get right — those were timing failures, not knowledge failures, and the distinction is invisible on a score report.
- Write one sentence for each wrong answer saying why it was wrong. Not "careless". An actual sentence, such as "I solved for x when it asked for 2x".
- Assign each a cause: content gap, method error, misread question, or out of time.
- Tally by domain and skill. Errors almost never spread evenly — two or three cells usually dominate, and those are the next fortnight's work.
- Keep the tally. After the next test, compare profiles rather than scores.
The error analysis guide covers the four causes and their different fixes in more detail.
How to tell it is working
Not by the total, which moves slowly and noisily and can sit still for weeks while real progress happens underneath it. Compare error profiles. If the skills that dominated the previous profile have shrunk in this one, the plan is working, even when the score has barely moved. If the profile looks the same as last time, the problem is what happened between the tests — and taking another one will not fix it.
The short version
Four to ten across a whole preparation, depending on its length. At least a fortnight between them. Official adaptive tests for measurement. The last one a week out. And an hour of honest error classification after every single one, because that hour is where the score actually comes from.
If you have not yet established a baseline, start with a diagnostic rather than with a practice-test schedule.