im going to apply for a o-a visa in the next few weeks, the plan is to stay in thailand for a couple of years at least. 

my passport is due to expire in july 2018, 

would it be better to renew now, or wait and renew later on while in thailand?

While the O-A visa in the old passport would remain valid after passport renewal, it would be simpler IMHO to renew your passport before getting the visa. This will avoid the necessity to transfer permission to stay stamps, and show both passports sometimes in the future.

I renewed my passport almost one year early.  Then i applied for the O-A visa.  It just makes things less complicated for the future.

If you apply for a new passport you will get 9 months added to its validity.

I think you are British.

11 minutes ago, Phuket Man said:

If you apply for a new passport you will get 9 months added to its validity.

I think you are British.

If in the UK it would certainly be easier to get a new passport now than waiting until you are here. To apply here requires 2 trips to Bangkok and a lot more paperwork (for example color copies of every page of your passport).

 

Phuket Man pointed out a key distinction between an early renewal between the UK and the USA.  In the USA I have renewed my passport early twice and both times I have gotten the full 10 years of validity on new passports.  It appears the UK will only add 9 months of validity on an early renewal.  

8 minutes ago, sqwakvfr said:

Phuket Man pointed out a key distinction between an early renewal between the UK and the USA.  In the USA I have renewed my passport early twice and both times I have gotten the full 10 years of validity on new passports.  It appears the UK will only add 9 months of validity on an early renewal.  

Since I have been in Thailand I have renewed two UK passports prior to their expiry date (full up). On each occasion I received the standard 10 years plus a 'bonus' nine months extra.

10 minutes ago, sqwakvfr said:

Phuket Man pointed out a key distinction between an early renewal between the UK and the USA.  In the USA I have renewed my passport early twice and both times I have gotten the full 10 years of validity on new passports.  It appears the UK will only add 9 months of validity on an early renewal.  

If not clear, this means you receive a new passport with 10 years 9 months validity. In my case, it is almost inconceivable that my passport would last that long before being full and needing renewal anyway.

10 minutes ago, sqwakvfr said:

Phuket Man pointed out a key distinction between an early renewal between the UK and the USA.  In the USA I have renewed my passport early twice and both times I have gotten the full 10 years of validity on new passports.  It appears the UK will only add 9 months of validity on an early renewal.  

Actually the UK does it better than the US. The new passport would be issued for 10 years and 9 months if there was 9 months of validity or more left on the old passport instead of only 10 years.