Hello all,

My company has a business model very similar to cellphone companies; a physical product is sold which is associated with a monthly tariff for a 12 or 24 month contract period. The monthly tariff is fixed price.

We have created agreements in OpenERP for the monthly contracts which works great for monthly invoicing.

The challenge is that we only want to invoice the customer once per month for all tariff payments. However if a new agreement has been signed in that month, we need to pro-rata the monthly tariff payment to only bill for the X days of the month where the tariff was active. The calculation would be ((monthly tariff price) / (days in month)) x active days = pro-rata payment due. Subsequent invoices would be for the full months fixed price.

I tried to post a link to an example but have insufficient karma. If you google for "optus pro-rata billing" the first page has a good explanation of how this works for cellphone companies.

I've read all the docs and spent ages Googling but I cannot find any hints/tips on how to implement pro-rata agreement invoicing in OpenERP.

I appreciate any help you can offer.

Thanks.