Hi. I would like to apply for an MeTV (multi entry tourist visa) online from the Thai embassy in London. 
 

I wondered when the date of the visa starts from.
 

Is it from when I enter Thailand and passport is stamped or is it from the date the visa is issued from the embassy. if it’s the latter,   for example If you took 4 weeks to travel from the date of receiving your visa in that case you would have 3 weeks less of the maximum time allowed with the visa?
 

thanks for any information. 

A visas validity starts from the day it is issued. For a (METV) that is 6 months.

When applying for a multiple entry visa it is best to try have it issued shortly before you start your trip.

As noted by @ubonjoe, the visa is effective from it's issuing date. I am on my third METV and was delighted to learn that, at least in the US, it is now issued as an e-visa, which means being spared the expense and time of mailing the passport and other documents which added 10-12 days to the process. My e-visa was approved and downloaded in three days. Of course there's no knowing the future, but had I known I would have had an extra 10-12 days of validity from the time is my arrival in Thailand.

2 hours ago, sureno said:

I wondered when the date of the visa starts from.

You have good answers above.

Aside, (and I'm sure that you would be aware) by exit and reenter just prior to the validity of your METV, you would be stamped in for another 60 days.

Of course each entry can be extended by 30 days.

Effectively it gives almost 9 month stay. 

Ripper visa option. 

The validity period for the Visa as mentioned is 6 months from date of issue.  However, your permission to stay in Thailand be 60 days from the date of entry which can be extended for another 30 days at Thai Immigration.  If you depart and return to Thailand prior to the expiration date of the "Visa", you again receive 60 days which can again be extended. 

 

For example, if your METV "Visa" expires on October 15, 2022 and you enter Thailand on October 14, 2022, your permission to stay stamp will be until October 12, 2022 and extended for an additional 30 days until January 12, 2023.

Thanks a lot for all answers. Really helpful.