I buy often a “+7” BKK transport ticket which is not very well known even by the clerks themselves. And yet it is so practical.
The scenario is the following: your monthly pass is about to expire and you will be on holidays in a week. What do you do? Buy a monthly pass that will not be used for a large part of its validity? Buy a weekly pass which costs HUF 4,900?
The better answer is: buy a “Kiegészitö heti Budapest-bérlet természetes személyeknek“, which is just a 1-week supplement to a monthly pass and cost only HUF 2,450.
The trick is to do it the very same day of the expiration of your monthly pass, at any hour, and with a clerk (impossible to buy with automatic machines) who will replace your monthly pass by this one-week supplement pass. I advise also to write down the name and price of this great ticket because some clerks are not familiar with this request, especially coming from a foreigner.