bhomburg

I did a lot of research on this topic a few years ago when moving over from LH/M&M where I got burned with miles expiring ever so often. Revisited lots of links and updated the info - here's my 2c:

Point expiration policies with OW programs are divided into two groups who follow different models.
AA, BA, IB, QF and US's programs govern expiration by general activity: Any activity (earning or redeeming points in any way) will keep ALL points in your account alive and reset the expiration counter for a set period of time.
AA, US and QF have set this activity requirement as at least once every 18 months, while BA and IB require qualifying activity only at least once every 36 months to reset the expiration clock.
For the not-so-very-frequent flyers all programs based on this model are OK, with a distinct advantage for the 36-month date of the IAG airlines (BA/IB).
Both AA and US offer options to reinstate expired miles for a fee: max. USD 400 (for 100k and more) will reinstate an expired Dividend Miles balance, max. USD 600 (for 75k and more) will reinstate an expired AA balance. US also has a cheap option to keep a balance alive by way of a $9 reinstatement fee that will keep the whole balance active for another 18 months after 15-17 months of inactivity.

The other camp lets their points expire around three years after they were earned. Here's the rundown, sorted by strictness:

TAM Fidelidade points expire after two years.
S7's priority miles generally expire at the end of the year in which they were earned, but validity may be extended up to two additional years for 'active members' (fly <3 segments on S7 metal, fare class restrictions apply) for a maximum validity of 36 months.
RJ's Royal Plus miles expire after 30 months.
AY's Plus points, JAL's JMB and UL's Flysmiles miles expire after 36 months.
CX's Asia Miles and AB's topbonus miles remain valid for 36 months, expiring at the end of the quarter in which they were collected - giving you up to 38 months of validity.
QR's Qmiles are valid for 3 years and will expire twice a year by the end of the semester (30th June and 31st December) in which they were earned, thusly giving you up to 41 months of validity.
MH's Enrich Miles are valid for the year in which they are earned plus an additional 3 years - they expire at the end of the third year, effectively giving you up to 47 months of validity.

LAN's Lanpass is something of a hybrid between both models: Kilometers earned by flying are valid for a period of 36 months after they are earned. Kilometers earned by using the services of LANPASS-associated businesses are valid for three calendar years. Independent of the limitations stated above, If you fly with LAN and earn one or more kilometers for the flight, ALL your kilometers will be revalidated for another 36 months..


What I'd do if I lived in Finland and wanted to build a points balance that won't expire even with minimal flight activity:
Switch to BAEC and get an MR-earning Amex card. Amex MR points can easily be transferred to BA Avios. All Avios earned through CC spend transfers will reset the expiration counter. This practically keeps your Avios balance from ever expiring even when you don't fly at all. Check this thread for more info.

edit: One word of caution - FF miles/points are subject to devaluations (just witness what UA did with their program recently or what LH did to M&M over the last decade). These happen with relatively little (if all) advance warning. It is generally considered best practice to NOT hoard tons of them for years and years, stashing them for retirement or whatever. And rules may change at a whim as well - QF changed the validity period from 36 months to 18 months back in 2010 for example. And airlines might not be around forever - anyone remember Qualiflyer?