One of the user using the “Terms of Payment” and updated the number of months in the “Months” field with the below setups.
>Selected the “Payment day”.
>Selected payment schedules.

Once created the invoice journal then select all mandatory fields and then selected the invoice date “6/30/2020” for example.

Example:
Invoice date = 6/30/2020
Terms of payment = 3 months
Payment date = 10th of each month.

Calculated Due date = 9/10/2020

Here, it is not calculating completed 100 days as per the terms of payment and payment day setup.

“Due date” is not updating correctly on the invoice journal as per the setup of “Terms of payment and Payment Day”, if using the Month option in the Terms of payment.

Would expecting to show the the Calculation Due date as "10/10/2020".

Please looks into this new idea request and share your suggestions along with Votes to consider for the future updates.