One hundred equally likely labels
A d100-style result chooses an integer from 1 through 100. Each named number has probability 1%, making the output convenient for percentile tables and chance statements already written as whole percentages. The mean is 50.5, which describes the center of many trials rather than a preferred result for one draw.
A percentile table check
If a table says outcomes 01 through 60 are ordinary and 61 through 100 are unusual, a shown 73 lands in the unusual band. Before the draw, that band contains 40 numbers and therefore has 40% probability. Counting inclusive endpoints matters: 61 through 100 is forty values, not thirty-nine. The interpretation comes from the table's intervals, not from the number's appearance.
Percent is a label, not a guarantee
A 73 on a percentile table does not mean something is 73% likely after it appears. The chance was defined by the set of 100 possible labels before selection. Some games create such a value with two ten-sided dice, while software can select directly from 100 integers; either method needs a stated convention for 00 and for whether 100 is included.
Where a d100 model is unsuitable
A uniform 1-to-100 draw does not represent a measured percentage, a weighted prize pool, or a probability with decimal precision. It also cannot combine a percentile roll with a modifier unless the rule tells you how to cap or wrap the result. Use it when every whole-number table entry is deliberately equal.
Inclusive endpoints are part of the formula
A range written 1 through 100 contains exactly 100 integers. If a table reserves 1 through 5 for one event, that event occupies five percent of the space, including both endpoints. Off-by-one mistakes usually come from forgetting that a visible interval includes its first and last labels, not from the random selection itself. Count the listed labels rather than estimating their share from punctuation or typography.
Questions about this dice rule
How likely is a particular number?
Each integer from 1 through 100 has a one-percent chance.
Is 00 always 100?
Paired-die notation differs by ruleset, so use its stated convention.