It depends on the format. On 60,000 real answer sheets, a 20-question yes/no format gave the same person the same letter about 65% of the time per scale; this test’s 12 hand-picked five-point statements per letter reach about 81% (estimated). Because the four letters multiply, even that leaves fewer than half of people with all four letters unchanged.
What “accurate” means here
There is no blood test for personality, so nobody can check your letters against a true answer. What can be checked is whether a test agrees with itself: give the same person two equivalent sets of statements and see whether they land on the same side of each scale. If a test cannot do that, nothing built on top of it holds.
The other half of the question is whether the scales measure something real. The four MBTI scales line up with four traits from the Big Five, the most studied model of personality: E/I with extraversion, S/N with openness, T/F with agreeableness and J/P with conscientiousness (McCrae and Costa, 1989). That is why a test built from public Big Five research statements can measure the same four preferences. MBTI is a registered trademark of The Myers-Briggs Company; this site is not affiliated with it.
How often the same letters come back
We ran the check on 60,000 real answer sheets from Johnson’s public IPIP-NEO data, whose reference group holds more than 135,000 people. For each format we drew two non-overlapping sets of research statements, 40 times over, and counted how often the same person got the same letter from both sets.
| Format | All four letters the same | Same letter, per scale |
|---|---|---|
| 2 five-point statements per letter (8 questions) | 15% | 62% |
| 5 yes/no questions per letter (20 questions) | 18% | 65% |
| 12 yes/no questions per letter (48 questions) | 28% | 73% |
| 8 five-point statements per letter (32 questions) | 31% | 74% |
| 15 yes/no questions per letter (60 questions) | 32% | 75% |
| 12 five-point statements per letter, random research statements (48 questions) | 38% | 78% |
| 12 hand-picked five-point statements per letter, this test (48 for the four letters) | about 44% (estimated) | about 81% (estimated) |
Two things stand out. A short test and a yes/no format each cost agreement on their own, and the gap between the weakest and strongest format is wide: 15% against about 44% for getting the whole four-letter type back. If you want the length and format question on its own, it has its own post.
The four letters multiply
A per-letter figure sounds reassuring until you remember a type has four of them. Each letter is a separate chance to flip, and the chances stack. At 65% per letter, fewer than one person in five keeps all four. Even at about 81%, the best figure here, fewer than half do. No four-letter test can promise you the same type every time, and one that does is not telling you how it was checked.
Six letters, as on this site, multiply once more. Cut every scale hard down the middle and only 28% of people would get all six letters back. That number is the reason this test does not cut hard down the middle.
Why your type “changes”
Most of the time your personality did not change; the measurement did. Four things usually explain a different result.
You were close on a scale. If your answers put you near the middle of E/I, either letter can come out on a given day. A test that forces a side turns that coin toss into a label. Here, a close call gets a few more statements on that scale, and if it stays close the result says in between. With that rule, about 7 in 10 people would see none of their clear letters flip to the opposite side on a retake, and on any single scale only 4 to 7% see a clear letter flip.
The test was short, or yes/no. Two statements per letter cannot tell a mild lean from a strong one. Yes/no answers throw away the difference between “a bit like me” and “exactly me”.
You answered as a different self. Who you are at work, who you want to be and who you were last week give different letters. Answer for how you usually are.
The tests used different statements. Two sites can both label a scale N/S and ask about quite different things. Compare a result only with a retake of the same test.
An INFP who comes back as an INFJ has most likely moved on one close scale, not become a different person. A retake here tells you which letters moved, never that “your type changed”.
How we measured
The figures above are a simulation, not a promise, and three things flatter every row.
- Both sets of statements were answered in the same sitting. That makes these upper bounds; a real retake weeks later agrees less.
- Letters were split at the middle of each format’s own results. This is generous to yes/no formats.
- The short formats were built from validated research statements. Many quiz sites write their own questions instead, so the short rows are if anything too kind to them.
The last row of the table is a model estimate rather than a measured figure. The same model reproduced the random-12 row within half a point (78.0% against 78.3% measured), which is why we trust it enough to publish. The full account, including where the statements come from, is on the method page.
What to look for in a test
- Five answer options, not yes/no.
- About 12 statements per letter. Beyond that, gains are small.
- Statements from a published research pool such as the International Personality Item Pool, started by Lewis R. Goldberg, rather than written for the quiz.
- A result that admits close calls instead of forcing a side.
- A plain account of how the test was checked, with its limits stated.
- No account, email or subscription before you can see your result.
Ready to see how your letters hold up? Take the test, about 10 minutes, no sign-up.