> ## Documentation Index
> Fetch the complete documentation index at: https://docs.getlago.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Plan model

> The plan model defines when and how much a customer is charged.

## Plan interval[](#plan-interval "Direct link to heading")

The plan interval corresponds to the billing period and defines when invoices
are generated. In most cases, the [charges](/guide/plans/charges) are also calculated
according to the plan interval.

There are several plan intervals:

1. **Weekly**: subscription fees and charges are billed on a weekly basis
   (Monday to Sunday);
2. **Monthly**: subscription fees and charges are billed on a monthly basis;
3. **Quarterly**: subscription fees and charges are billed on a quarterly basis (every 3 months);
4. **Semiannual**: subscription fees and charges are billed on a semiannual basis (every 6 months); and
5. **Yearly**: subscription fees are billed on a yearly basis and charges can be
   billed monthly or annually.

## The base charge amount and its currency[](#the-base-charge-amount-and-its-currency "Direct link to heading")

You need to define a **base amount** for each plan (i.e. the subscription fee).
This amount is what the customer will pay by subscribing to the plan regardless
of their consumption.

This base charge `amount` is recurring, and billed at the end of each billing
interval.

## Pay in advance or in arrears[](#pay-in-advance-or-in-arrears "Direct link to heading")

With Lago, you can define if the base charge of the Plan is paid **in advance**
or **in arrears**.

* If the toggle is `off` (boolean set to FALSE), the Plan is paid for the past
  period (in arrears).
* If the toggle is `on` (boolean set to TRUE), the Plan is paid upfront (in
  advance) for the period.

<Note>
  Note that this toggle only affects the base amount of the Plan. Additional
  charges for per-usage Billable metrics **are always paid in arrears because
  they are linked to a past consumption of your customers.**
</Note>

## The trial period (optional)[](#the-trial-period-optional "Direct link to heading")

You can decide to apply a `Trial period` for a Plan. This means your customers
can test the Plan without being charged for a certain number of days. This is
optional and if the value is null, the Plan holds 0 day of trial.

Note that the trial period **can only be specified in days**. A pro-rata is
applied to the Plan regarding the number of days offered.

<Warning>
  A trial period can only be applied to the first subscribed Plan. In case of an
  upgrade or downgrade, the trial period of the new Plan **is not applied**.
</Warning>

<Warning>
  The trial period is only applied to the subscription fee.
</Warning>

Any events received during the trial period will be taken into account at the end
of the billing cycle. Pay-in-advance charges will be invoiced and collected immediately
after an event is received.

If you want maximum flexibility, you can define two different Plans: one for the
free trial and one regular plan. A new customer starts on the free plan, and you
can configure the regular plan to start after the trial period. The free plan
subscription will automatically be terminated when the regular plan starts.

## Taxes applied on plans or charges

You have the option to store taxes either at a Plan level or for specific charges.
This choice entails that whenever you apply this plan to a customer without taxes,
invoice fees will inherit the taxes defined in the corresponding plan.

<Info>
  It's important to acknowledge that taxes applied to a plan will influence the charges,
  unless the taxes are explicitly defined for the individual charge.
</Info>

## Pro-ratas based on subscription date[](#pro-ratas-based-on-subscription-date "Direct link to heading")

Obviously, we know that your customers don't necessarily sign up for a Plan at
the very beginning of each month (or each year). This is why Lago automatically
applies a pro-rata for the first and the last subscription period of a Plan.

Here is an example: A `Customer X` signs up for the Plan `Start` (base amount of
10€, with no trial period) on April 15, 2022.

* If the Plan is defined to be `paid in arrears`, this Customer will be charged
  5€ for the first month at the end of the period (May 1, 2022).
* If the Plan is defined to be `paid in advance`, this Customer is charged 5€
  straight away for the first month (April 15, 2022).

<Note>
  Note that pro-ratas can also be applied in case of **upgrades or downgrades**.
</Note>