Assuming that you would be working 2/3 of the time in your entire life, you should be saving at least 1/3 of your pay. The key word here is AT LEAST. Bcos we must not forget inflation.
Now say if you are currently 30 yrs old, you earn $3000 per mth, you expect to retire at 60 and live until 75, i.e. you work 30 yrs out of 45 yrs of your life (2/3) and have no income for the last 15 yrs (1/3 of 45). You should be saving at least 1/3 of your pay i.e. $1000 in order to maintain your current lifestyle until the day you go to heaven (or wherever you want to go that won't need money from Earth... hehe).
Why is this so? Bcos the 1/3 that you save for 30 yrs (which amts to $1000 x 12 x 30 = $360,000) will be just enough to cover you for the next 15 yrs when you don't work at all ($360,000 /(15 x 12) = $2000 = the amt you are spending now every mth). That is assuming no inflation.
Hence similarly if you want to retire at 50 and die at 70 (which means you work 20 yrs and don't work 20 yrs) you would need to save at least 50% of your pay. Which probably means 90% of Singaporean cannot retire at 50 and die at 70, bcos if they want to retire at 50 they must die, say at 55 in order not to rely on their children or the state or any other entity to support them. How fun.
So what happens when we take inflation into account? Well it simply means you have to save more, or make your money work harder (i.e. invest lor). If inflation is 3%, then for every dollar you save, it must earn 3% every year until you retire. If you believe in this blog which says investment earns 8%, then all is well.
If you intend to cover inflation by saving more, it gets tricky bcos inflation goes on yearly but you only save the same amt every month. This means that for Year 1 you will need to save 3% x 30 (yrs) = 90% more and Year 2 you need to save 3% x 29 (yrs) = 87% more and so on (i.e. Year 1 you need to save $1900 per mth, Year 2 you need to save $1870 per mth and so on).
But you only earn $3000 per mth remember? How to save $1900? It cannot be done, so the answer is you should spend less, much lesser than the original $2000 per mth. As a rule of thumb, I think saving 50% of your salary should be quite ok. Which then means a lot of pple in Singapore are probably not ok... Count on me Singapore, count on me to go broke before 50!
See also Investment cannot make you filthy rich