I turn 66 next month (July 2018). I recently became self-employed. I am married and have more than 40 quarters of work in covered employment. My wife is an employee, she will turn 59 next month, and she has also has more than 40 quarters of covered employment. I tend to continue to work until I am 70 and that is when I plan to file for my SS benefits. My wife does not plan to file for her benefits before age 70. Is there a benefit for either of us to file for spousal benefit, and if so when should we file? I don't know if it matters but we each earn more than $150K per year.
There are only 2 ways that either you or your wife could become eligible for spousal benefits. One is if either of your full retirement age rates (PIA) is higher than the other spouse's PIA. In that case, the spouse with the lower PIA could be eligible for an unreduced spousal rate of 50% of their spouse's PIA minus their own PIA.
The other possibility is that you could become eligible for just spousal benefits only prior to filing for your own benefits. However, your wife would have to be drawing her benefits in order for you to qualify for a spousal benefit, so she would have to either be 1) at least age 62 and drawing retirement benefits or 2) be drawing Social Security disability benefits. BTW, your wife could never file just for spousal benefits only on your record because she was born after January 1 1954 (https://www.ssa.gov/planners/retire/deemedfaq.html).
Whether or not filing for spousal benefits and when to file for those benefits depends on your and your wife's relative benefit rates as well as your personal preferences. I would strongly suggest that you and your wife use our maximization software in order to explore and compare all of your various filing options to determine your best overall strategy.