# Dynamic values The `value` key of a condition can be *dynamic* — useful when the value to be compared against the `field` isn't known in advance, or depends on another field in the payload. To leverage dynamic values for a rule's conditions, you need to wrap the reference field in double curly brackets: `{{}}` where `` is the resource's field (expressed in dot notation) that will be used as a variable to calculate the value. You can also apply some basic aggregation operators to the reference field (as shown in the [examples](#examples) below):

Operator	Field type	Description	Example value
`min`	Number	The smallest of the reference field values is used as the condition's value.	`"{{min(order.line_items.shipment.available_shipping_methods.price_amount_cents)}}"`
`max`	Number	The biggest of the reference field values is used as the condition's value.	`"{{max(order.line_items.compare_at_amount_cents)}}"`
`avg`	Number	The average of the reference field values is used as the condition's value.	`"{{avg(order.line_items.sku.inventory.levels.quantity)}}"`

{% hint style="info" %} The reference field type must be consistent with the [matcher](/rules-engine/matchers.md) used against the field and value. Given the currently available functions, if you want to add one of the operators above, the reference field type must be numeric. {% endhint %} ## Examples ### Direct dynamic value The following condition uses a dynamic value to check if an order's line items have the same unit amount and *compare-at* amount (i.e. the actual selling price is equal to the full price displayed to the customer with a strikethrough — meaning the item is not on sale):

"conditions": [
  {
    "field": "order.line_items.unit_amount_cents",
    "matcher": "eq",
    "value": "{{order.line_items.compare_at_amount_cents}}"
  }
]

### Dynamic value with operator The following condition uses a dynamic value with the `min` operator to target the shipment line items associated with the cheapest shipping method among the ones available for an order's shipments:

"conditions": [
  {
    "field": "order.line_items.shipment.cost_amount_cents",
    "matcher": "eq",
    "value": "{{min(order.line_items.shipment.available_shipping_methods.price_amount_cents)}}"
  }
]

## Date-based values Dynamic values also support date expressions, making it straightforward to write conditions that are evaluated against the current date or against a date field from the payload. This is particularly useful for time-sensitive promotions — such as birthday discounts, seasonal offers, or deals tied to specific order timestamps — without hard-coding any dates in your rules. Date expressions follow the same double curly brackets `{{...}}` notation. The available functions accept a `` argument and optionally an ``:

Expression	Field type	Description	Example value
`today`	Datetime	The current date (UTC), resolved once per rule evaluation. It's a costant, no additional argument accepted.	`"{{today}}"`
`day(<date>)`	Datetime	The day of the month (1 – 31) extracted from `<date>`. When used as a value, the engine compares the day part of the `field` date against this number.	`"{{day(today)}}"`
`month(<date>)`	Datetime	The month (1 – 12) extracted from `<date>`. When used as a value, the engine compares the month part of the `field` date against this number.	`"{{month(order.updated_at)}}"`
`year(<date>)`	Datetime	The year extracted from `<date>`. When used as a value, the engine compares the year part of the `field` date against this number.	`"{{year(today)}}"`
`{{birthday}}`	Datetime	Matches any date whose day and month equal today's, regardless of year. A year-agnostic shorthand for combining `{{day(today)}}` and `{{month(today)}}` in a single expression.	`"{{birthday}}"`
`{{range(<date>, <interval>)}}`	Datetime	Defines a date window of `±<interval>` around `<date>`. Learn more here.	`"{{range(today, 7.days)}}"`

The `` argument can be either: * A **constant** — `today`, which resolves to the current date (UTC) at evaluation time. * A **payload field path** — any date or datetime field from the current payload, expressed in dot notation (e.g. current order's timestamps such as `order.created_at`, `order.updated_at` etc.). The value is resolved per subject from the payload. {% hint style="info" %} Even if all date expressions operate on `field` values of type *Datetime*, when a date-part function is used as the value (e.g. `{{month(today)}}`), the engine automatically extracts the same part from the field date before comparing — no additional operator is needed on the field side. {% endhint %} ### Date ranges The `range(, )` expression resolves to a pair of dates representing a symmetric window centered on ``: ``` [date - interval, date + interval] ``` {% hint style="info" %} Because the value is an array of two dates, it must always be used with the `gteq_lteq` matcher, which checks that the `field` date falls within the range (inclusive on both ends). {% endhint %} The `` must follow the format `n.`, where `n` is a positive integer and `` is one of `days`, `months`, or `years`. For example: * `{{range(order.updated_at, 7.days)}}` — 7-day window around the order's latest update * `{{range(today, 2.months)}}` — from 2months ago to 2 months from now * `{{range(today, 1.year)}}` — from 1 year ago to 1 year from now ### Examples #### Birthday month discount The following condition lets you apply a promotion to all customers whose birthday falls in the current month by comparing the month of the `birthdate` field in the customer's metadata with the current month (i.e. the engine extracts the month from `customer.metadata.birthdate` and checks whether it equals the current month as integers):

"conditions": [
  {
    "field": "customer.metadata.birthdate",
    "matcher": "eq",
    "value": "{{month(today)}}"
  }
]

#### Birthday discount (exact day and month) You can activate a promotion on a customer's actual birthday by combining two conditions:

"conditions": [
  {
    "field": "customer.metadata.birthdate",
    "matcher": "eq",
    "value": "{{month(today)}}"
  },
  {
    "field": "customer.metadata.birthdate",
    "matcher": "eq",
    "value": "{{day(today)}}"
  }
]

To do that, you can also leverage the `birthday` shorthand:

"conditions": [
  {
    "field": "customer.metadata.birthdate",
    "matcher": "eq",
    "value": "{{birthday}}"
  }

#### Promotion for orders created in a specific date range The following condition lets you activate a promotion for orders created within a 15-day window around the current date:

"conditions": [
  {
    "field": "order.created_at",
    "matcher": "gteq_lteq",
    "value": "{{range(today, 15.days)}}"
  }
]

#### Match birthdate month with the order creatiom month The following condition lets you apply a discount when the customer's birth month coincides with the month in which the order was created (i.e. the engine extracts the month from both the `field` date and the value expression, then compares them as integers):

"conditions": [
  {
    "field": "customer.metadata.birthdate",
    "matcher": "eq",
    "value": "{{month(order.created_at)}}"
  }
]

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