Whatever number you have in your mind it just went up $1000 a year because that is how much a retirees' cost of living rose in the past 12 months according to updated research from the Association of Superannuation Funds of Australia (ASFA) and Westpac.

To put that into annual income terms a couple enjoying a "comfortable" lifestyle will need about $46,200 a year while a single woman satisfied with a "modest" lifestyle will need around $18,000.

Now it is obviously subjective what equals a "comfortable" versus a "modest" lifestyle but the extra things that are added into these calculations - much of which was done by the Social policy Research Centre of the University of New South Wales - include things like a kitchen or bathroom upgrade to the home at some stage, some wine, better clothes from upmarket shops, computer and home entertainment items, top rate health cover, a more expensive car and occasional overseas holidays.

The Westpac-ASFA living standard benchmarks are updated quarterly and are a good reminder that retirees are not immune from cost of living increases and how important it is for retirees to budget for rising costs - particularly things like health care, food and petrol. Interestingly in the past year while essentials like petrol have seen a 15% rise and food is up 3.6% luxury goods like audio, video and computers have fallen by 6%.

The "modest" lifestyle modeled by ASFA/Westpac is a step up above the age pension - now $12,800 a year for a single person - while a "comfortable" lifestyle is a step up again.

There is other research work - a study by CPA Australian and Natsem for example - that came up with similar income requirements so if we accept these figures then it allows us to work back to understand how much you need as a lump sum at the time of retirement to generate the type of income these research studies suggest is necessary.

Take a couple looking for the "comfortable" retirement. They are 40 years old today, plan to retire at 65, have $50,000 in super already and earn $60,000 a year.

Using a calculator developed by independent actuaries Rice Walker and assuming a 7% investment return (after fees) our couple would have super savings of $319,000 at age 65 in today's dollar terms. This assumes inflation is 3%, their salary increases in line with inflation and the employer contributes the minimum 9% super guarantee.

If our couple spent the $46,200 a year then the money could be exhausted by age 74.

So the comfortable lifestyle would last less than 10 years and they would quickly find themselves having to fall back on to the age pension.

A single woman of 40 with the same existing super balance and salary level but content with a "modest" lifestyle that would need $18,000 a year according to ASFA/Westpac would be able to make the same lump sum last another 21 years to age 95.

What makes the question "how much is enough?" so hard to answer is the number of variables in the mix - investment markets, spending habits, your health and even where you live. There are a lot of calculators on various websites and it is critical to take the time to understand the assumptions because small differences can have major impacts over long time periods.

Add to those variables the positive news that you are likely to live longer which means you have to decide how long your money has to last - it could be age 85 or just as easily be 90. If you are grappling with that you can see why financial planners have such a hard time giving anyone a definite answer.

So what would it take for our 40-year-old couple to fund a comfortable lifestyle at least until age 85? Inevitably it means trading off some of today's lifestyle for future peace of mind. If our couple increased their super contributions significantly by salary sacrificing $8500 a year - more than doubling the mandatory 9% super guarantee level - their lump sum at age 65 would be around $616,000 which is projected to be enough to fund the "comfortable" level of retirement until age 85.

The harsh reality is that nobody can give you a definitive answer to the question of how much is enough. But what is absolutely clear is that ignoring the question altogether is not the answer either.

* The calculator used to provide these examples is available on Vanguard's website.