> For the complete documentation index, see [llms.txt](https://docs.internetobject.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.internetobject.org/structure-and-syntax/values/number/decimal.md).

# Decimal

A **Decimal** is a fixed-precision decimal value for cases that demand exact numbers — especially financial calculations, where floating-point approximation can introduce errors. A Decimal stores an exact value with a defined precision and scale.

Unlike a standard floating-point Number, a Decimal does not approximate: `0.1m` is exactly one-tenth, not the nearest binary fraction.

## Syntax

A Decimal is written as a number with the `m` suffix. It requires a leading digit and, if a decimal point is present, at least one digit after it. Scientific notation is **not** supported.

```ebnf
decimal = ["-" | "+"] digit+ [ "." digit+ ] "m"

digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
```

## Structural characters

| Symbol  | Name           | Unicode  | Description                                |
| ------- | -------------- | -------- | ------------------------------------------ |
| `m`     | Decimal suffix | `U+006D` | Marks the value as a Decimal               |
| `0`–`9` | Digits         | Multiple | Decimal digits                             |
| `.`     | Decimal point  | `U+002E` | Separates the integer and fractional parts |
| `-`     | Minus sign     | `U+002D` | Negative value                             |

## Valid forms

```ruby
---
123.45m, 123m, 0.001m, -789.01m, 0m, 0.0m
```

* `123.45m` — fractional decimal
* `123m` — integer decimal
* `0.001m` — leading zeros preserved
* `-789.01m` — negative decimal
* `0m`, `0.0m` — zero, with and without a scale

## Precision and scale

Each Decimal carries a **precision** (the total number of significant digits) and a **scale** (the number of digits after the decimal point):

```ruby
123.45m              # precision 5, scale 2
0.000123m            # precision 6, scale 6
```

A schema can constrain these; see [Decimal](/schema-definition-language/data-types/decimal.md).

## Invalid forms

A Decimal requires a leading digit and, with a decimal point, a trailing digit. Scientific notation is rejected:

```ruby
---
1.23e2m              # ✗ scientific notation is not supported for Decimal
```

```ruby
.45m                 # ✗ missing leading digit (use 0.45m)
123.m                # ✗ missing trailing digit (use 123.0m or 123m)
123.45mm             # ✗ duplicated suffix
```

> A plain `123.45` (no `m`) is a valid **Number**, not a Decimal — the `m` suffix is what selects fixed precision.

## Preservation of structure

Internet Object preserves:

* Exact decimal precision and scale
* Syntactic fidelity as written, except that an explicit `+` sign is not preserved

It does **not** interpret:

* Rounding behavior for operations
* Currency or unit semantics

Those semantics belong to the schema, the validator, or the application.

## See Also

* [Numeric Values](/structure-and-syntax/values/number.md) — all numeric forms
* [Number](/structure-and-syntax/values/number/number.md) — standard floating-point numbers
* [BigInt](/structure-and-syntax/values/number/bigint.md) — arbitrary-precision integers


---

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