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Overview of charges

Fixed charges let you bill recurring fees that are not based on usage. They are tied to add-ons and sit outside the event stream. Common examples include platform fees, seat licenses, or support packages. Unlike usage-based charges, fixed charges are billed as a fixed recurring amount. The units defined on the fixed charge are used by Lago to generate the fee on the invoice.

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Charge models and billing behavior

Fixed charges support a limited set of pricing options compared to usage-based charges. They can use: They can be configured to:

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Currency

All fixed charges use the same currency as the plan, ensuring consistency across invoices.

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Trial period

Trial periods apply only to the plan’s base amount. Fixed charges are always billed, even during a trial.

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Decimals precision

Fixed charges can be defined with up to 15 decimal places (for example: $0.000123456789123). Fixed charges are invoiced in amount_cents, so Lago automatically rounds values when generating invoices (for example, USD 1102 amount_cents = $11.02).

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Edit a fixed charge

When editing a fixed charge, you can edit the amount and the unit already defined. You can choose when unit changes should apply:
  • Apply now: The new unit value is applied immediately. If the fixed charge is billed in advance, this may trigger invoice issuance.
  • Apply at next billing period: The new unit value is applied at the start of the subscription’s next billing period.
This gives you control over whether changes impact current or future billing.
Editing a fixed charge unit may generate invoices when the charge is billed in advance and changes are applied immediately.
Customers will receive an invoice reflecting this update.

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Update a fixed charge via the API

To update a fixed charge on a subscription, pass it under the plan_overrides object when you create or update the subscription. How you update it changes the outcome:
  • Pass only units (and apply_units_immediately if needed) to change the quantity. This does not create a plan override.
  • Pass any other field, such as a price or properties, and Lago creates a plan override.
This request updates the units only. It does not create a plan override:
Update units only (no override)
{
  "subscription": {
    "plan_overrides": {
      "fixed_charges": [
        {
          "id": "af360881-357a-4334-ad16-8cd38e246d03",
          "units": 20,
          "apply_units_immediately": true
        }
      ]
    }
  }
}
This request creates a plan override, because it changes the price:
Update price (creates an override)
{
  "subscription": {
    "plan_overrides": {
      "fixed_charges": [
        {
          "id": "af360881-357a-4334-ad16-8cd38e246d03",
          "units": 20,
          "properties": {
            "amount": "30"
          },
          "apply_units_immediately": true
        }
      ]
    }
  }
}
Send only units to change the quantity without creating an override. Any other field creates one.

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Delete a fixed charge

You can delete a fixed-charge even if the plan is associated to active subscriptions. Once deleted and saved:
  • The fixed-charge is immediately removed from all linked subscriptions
  • It is removed from all draft invoices.
However, the fixed-charge will still appear on invoices finalized before the deletion.

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Invoice display name

You can customize, during plan creation or edition, how a fixed-charge appears on invoices by setting an invoice display name. This name overrides the default fixed-charge name and is shown everywhere invoices are displayed.