Odoo cannot automatically pick “the 15th” as a billing day in templates, but it can follow the date you give it, and repeat one month later.

So we use:

Monthly (Prepaid) invoicing

→ This ensures the invoice covers the next month.

✔ Set Next Invoice Date = 15th of this month

→ After this, Odoo repeats every month on the 15th.

 Follow these steps (100% standard)

Subscription Template Settings

Go to:

Sales / Subscriptions → Configuration → Subscription Templates

Set:

• Recurring Invoicing = Monthly

• Invoice Timing = Prepaid (invoice at the beginning of the period)

  → This makes the invoice cover next month.

Example:

Invoice on 15 Dec → Coverage: 1 Jan – 31 Jan

 Set the first “Next Invoice Date” manually

Open any subscription created with this template → Edit:

• Set Next Invoice Date = 15 December 2025

This is the only time you must enter it manually.

 Activate the Built-in Cron Job

Odoo already has a scheduled action:

➡ "Subscription: Generate Recurring Invoices"

Runs daily.

On 15 Dec, the cron will see the subscription is due → generate the invoice.

 After that, Odoo does the rest automatically

You don’t need to touch anything again.

Odoo will repeat:

It always uses the same day % + prepaid logic.