# `YearMonth`

One month of one year: `2026-10`.

Use it for a billing period or a monthly report. For the month a card expires, use [`CardExpiry`](/docs/types/type-card-expiry.md). For a month in any year, use [`Month`](/docs/types/type-month.md).

## Shape

| Field | Type | Required? |
|---|---|---|
| `year` | `Int` | Yes |
| `month` | `Int` | Yes |

## Example

```jadpo
YearMonth { year: 2026 month: 10 }
```

`text.parse(raw, as: YearMonth)` reads one from text that comes from outside. Text that isn't one at all fails `malformed`, such as `2026-13`, `2026-00` or `2026-1`.

## Good to know

- `==` tells you whether two are the same, and `<` and `list.sort_by` compare and sort them.

## In JSON

A string, in a request, a response or `json.write`:

```json
"2026-02"
"2026-10"
```

## Details

<details>
<summary>Text form, storage, how it is shown, and operations</summary>

`YearMonth` is in the group Time and calendar, and has been in Jadpo since 0.1.0.

### Text form

`text.from` writes one standard text form, the same form `text.parse` reads back: `2026-02` and `2026-10`.

### How it is stored

It is stored in 2 columns, each named for the field, `_` and its suffix. This is `2026-10`:

| Column | Type | Holds |
|---|---|---|
| `<field>_year` | `smallint` | `2026` |
| `<field>_month` | `smallint` | `10` |

### How it is shown to people

`text.format(value, locale:)` shows it to people in their locale.

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `2026-02` | `February 2026` |
| `2026-10` | `October 2026` |

### Operations

It also takes `text.parse`, `text.from`, `text.format`, `json.read`, `json.write` and `==`. [How every standard type behaves](/docs/every-standard-type-meets-one-contract.md) says how they work.

</details>