What Is an Income Deviation Score
A deviation score (hensachi) expresses how far a value sits from the mean, measured in units of standard deviation. A score of 50 is the average, 60 is one standard deviation above, and 40 is one below. Familiar from school exams in Japan, this scale offers an intuitive way to sense where your income falls within the whole.
The score carries a strong assumption: that the data follow a symmetric normal distribution. Under that assumption a score of 60 maps exactly to the top 15.9% and 70 to the top 2.3%. Whether income actually permits this conversion is the crux of reading your position correctly.
Why the Average Income Exceeds the Median
In Japan, the median annual income for wage earners is roughly 4.1 million yen while the mean is about 4.9 million yen (estimates based on National Tax Agency and Ministry of Health, Labour and Welfare distributions). The mean exceeds the median by 800,000 yen because the distribution has a long right tail. A small number of high earners pulls the average up, while most people sit below the median.
The mean of 4.9 million yen actually lands near the 61st percentile, meaning about six in ten people earn below the so-called average. There is no reason to feel inadequate against an average that already diverges from what the majority experiences.
Why "Top X Percent" Beats a Deviation Score
Because income is not normally distributed, a deviation score understates the position of high earners. Consider fitting a normal distribution that reproduces the top 10% threshold of 9.5 million yen; the implied standard deviation is about 3.6 million yen. Yet that same normal curve predicts a top 1% threshold of roughly 13.25 million yen, far below the actual figure of 20 million yen.
The real upper tail is heavier than any normal distribution can describe. Since the deviation score assumes symmetry, it cannot capture this thick tail. To know your position accurately in a skewed distribution, the percentile, counting how many people earn less than a given amount, is the more reliable measure.
Percentile Thresholds for Common Incomes
Reading Japanese incomes by percentile, the milestones run roughly as follows: the bottom 10% at 1.5 million yen, the 25th percentile at 2.7 million, the median (50th) at 4.1 million, the 75th at 6.2 million, and the top 20% at 7.0 million yen.
Higher up, the top 10% sits at 9.5 million yen, the top 5% at 12 million, and the top 1% at 20 million. A deviation-score conversion would place the top 10% near a score of 63 and the top 20% near 58, but the top 1% would require a score well beyond 70, where the conversion breaks down. The gap between deviation score and percentile widens as income rises.
Do Not Confuse Gross with Net, or Household with Individual
The most common error in comparison is mixing gross income with take-home pay, or household income with individual income. The take-home from a gross 5 million yen is about 70%, roughly 3.5 million yen after social insurance and taxes. Rankings are distorted unless you compare gross with gross and net with net.
Conflating household and individual figures matters too. Comparing a dual-income household total against your own individual income makes you appear lower than you are. Confirming whether the reference distribution is individual or household, gross or net, is the precondition for reading it correctly.
Check Your Domestic Rank
The deviation score is only an entry-level yardstick; in the right-skewed income distribution, the percentile rank is what accurately reflects your position. MyRank's income ranking uses domestic data to calculate the exact percentile your entered income occupies within Japan. When you select gross income, it also adjusts to take-home pay, so you can compare without worrying about mismatched bases.
These figures represent a statistical position only and assign no superiority to higher or lower earnings. Use them to understand your current standing objectively and as material for thinking about household finances and how you work.