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 who takes a test every Saturday and never reviews one 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: review each test before you take the next
The number of tests matters less than what happens between them. A test that has been reviewed — every wrong answer redone, explained and given a cause — is worth taking. A test taken on top of an unreviewed one adds a second score and no new information.
Within that rule, more measurement is better, and the spacing should tighten as the exam gets closer: early on there is content to learn between tests, and at the end the job is exam stamina and pacing, which only full-length tests build. Twenty full-length tests, spread like this, cover the common preparation lengths:
- About 10 weeks: a diagnostic in week one, then about two a week, rising to two or three a week in the last three weeks.
- 16 weeks: a diagnostic, one a fortnight while content is being taught, then around three a week in the final five weeks.
- Six months: a diagnostic, one a fortnight for three months, then one to two a week in the last two months.
In every case the last full-length test goes three to five days before the exam: late enough to reflect where you are, early enough to review it. The final two days are for your own error log and for sleeping.
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 — a handful of tests — so a student testing regularly needs a second source in the same adaptive format. 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 or the difficulty mix that follows from it.
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
Up to twenty across a whole preparation, spaced further apart early and closer together at the end. Adaptive tests for measurement. The last one three to five days out. And an hour of honest error classification after every single one, before the next, 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.