64% of millennials are pretty sure they won't save enough money to retire

Roughly two-thirds of millennials don't think they'll have enough money to retire.

According to a new survey from Wells Fargo of 1,000 US adults between 22 and 35 - yes, 35-year-olds, you are millennials - 64% don't think they'll be able to save $1 million, often seen as a nest-egg target to fund a multi-decade retirement.

And considering that 74% of respondents don't think Social Security will be available to them at retirement, things are indeed bleak for today's young people who would one day like to not work.

Joe Ready, director of Institutional Retirement and Trust for Wells Fargo, notes, however, that millennials do have one thing on their side: time.

"Millennials may not realize that if they start saving consistently by their mid-twenties - and stay invested for the duration of their working years - they will likely accumulate $1 million by the time they retire," Ready said.

However!

Ready's advertised math looks, well, ambitious. Here we go:

"A millennial that earns a starting salary of $32,000 at age 25, saves 5% the first year and then increases their savings rate by 2% each year (up to 13%) could accumulate $1 million by age 65. This assumes the earner receives a 2% salary increase annually, is invested in the market and realizes a 7% return on their invested assets."

From 1928-2014 the annualized return for the S&P 500 is about 10%. This is good. This would make achieving a 7% return seem pretty manageable.

A paper from last August out of GMO, however, notes that retirees face what is called "sequence risk" when it comes to their retirement, meaning that when you start and stop matters a lot.

This is not to say someone is better off trying to time the market, but it highlights that in a world where retirement is shifting from defined benefit - things like pensions and Social Security where savers are promised some fixed regular payment after retirement - to defined contribution - typical modern 401ks where employers match an employee contribution to a savings account that gets invested in the market - market risk becomes more significant for savers. As you'd expect, in a world where savers are more exposed to the market's elements, those elements are more important.

And while some, like Business Insider editor-in-chief Henry Blodget, think the high valuation of the stock market today represents a risk that we could see a crash, what this valuation more conservatively reflects is the likelihood of lower future returns.

Ready notes that millennials do have the advantage of time, which this chart from Andy Kiersz makes obvious.

Time is good. What returns are during that time is less clear. History would say good, fine. Current conditions look less friendly.

And while this is definitely not investing advice, all investing advice comes with the disclaimer that past performance does not guarantee future returns.