You don't need to work for 14 more years under these assumptions. I can't recommend any online calculators, but I can do the math for you based on what you've already given us.
We can break your situation down into two time periods: before social security and after social security. After social security, you will be getting $39,600 per year in income from the government lowering your current $68,172 in expenses to only $28,572 that needs to be covered by investment income. Following the 4% safe withdrawal rate, you will need $714,300 in twelve years to sustain this spending level. At 7% interest you would need $714,300*(1.07)^-12 = $317,157.70 in today's money to secure this retirement income.
Congratulations! You already have enough to retire twelve years from now. If we reserve that $317,157.70 for later, we are left with $482,000 - $317,157.70 = $164,842.30 in unreserved savings.
That takes care of the period of time after social security, but what about the next twelve years, before social security? According to the above math and the information you provided, you have $164,842.30 in unreserved savings, a yearly income of $107,172, and yearly expenses of $68,172. What we need to figure out is how many years the $107,172 income will need to accrue to provide for twelve years of $68,172 in yearly expenses with $164,842.30 in current savings. Since we know that the $68,172 yearly expenses will occur each year for the next twelve years, we can find that the present value of these expenses is $541,468.81 at 7 % interest (for more information on how to calculate this look up time value of money and annuity valuation). That means we need $541,468.81 - $164,842.30 = $376,626.61 in salary discounted at the 7% rate. Using a salary of $107,172 we find that only 4.1733 years are needed to earn this much.
If you want to stay more consistent with your after social security withdrawal rate, then we can value the expenses at a 4% rate instead of 7%. In that case, $639,799.25 is the present value of your expenses over the next 12 years necessitating $474,956.95 in salary discounted at the 7% rate (since we're still assuming 7% ROI). 5.498 years will be needed to earn this much.
As always, keep in mind that real returns are not usually guaranteed, and fluctuations in ROI, especially during the early years of retirement, will affect how long your savings last. Also, the above example assumes level expenses and does not take into account taxes or inflation. Additionally, all calculations were performed using nominal yearly values compounded at the end of the year; in real life money would be going out or coming in at various time throughout the year. YMMV on how applicable these numbers are to your real world situation.
