Not that the news has been cheery onthe retirement front, with headlines blaring howunprepared most people are, but it could even be worse.

According to Forbes, there are a number of factors thatare undermining just how well people can gauge their preparedness.Among them is the use of rule-of-thumb estimates on how much peoplemay need to meet their expenses in retirement.

While aiming generally toward replacing 70% to 80% of yourincome may sound good enough — at least before you get close to thetime when those numbers will have to be validated — if you don'tconsider how much you personally may need, you could fallshort.

Studies have found that while most people spend about 14% lessin retirement than they did while they were working, 35% spendabout the same (so much for that 70% to 80%) and 12% actually spendmore.

Tracking your expenditures for several months as you get closerto retirement will help you get a better handle on what you mightneed — particularly if you consider such factors as whether youplan to travel more, or whether your car will need to be replacedonce you retire.

Then there's Social Security. Trusting what the Social Securitywebsite predicts you'll receive can be a dicey proposition, itsaid, pointing to the projection that the Social Security trustfund will be depleted by 2034. By how much might that reduce yourbenefits and how much are you counting on them?

Pensions might not be such a sure thing, either, since manycompanies are freezing pension plans — and if you can't stay withyour employer long enough to be vested, that will affect what youmight be able to draw on, too.

Oh, and if you're planning on a job during retirement, you mightwant to rethink that as a sure thing: 48% of retirees who want towork aren't, 35% are unemployed for health reasons, 5% provide careto a loved one and 8% just couldn't find work. Even if you plan towork until age 65 you might not be able to, due to ill health orbecause your job just disappeared. That means you'll have less timeto save and more time to spend.

Then there's the good news: You might live longer. The badnews: You might outlive your savings.

Then there are those pesky issues around your investments:Expected return (usually estimated high) and confusing investmentreturns with income. In the former case, projections of 7% to 10%returns are likely too optimistic, given low interest rates, marketvolatility and other factors. An estimate of less than 5% annuallywould be more realistic. Even if you make that 5%, though, thatdoesn't mean you can take the whole 5% out every year. Doing socould deplete the principal, which could run you out of moneysooner rather than later.