I've seen these points before about delaying SS until 66 or 70. In my view, they're lottery gambles to convince us to wait as long as possible, where a good percentage of folks will never realize, enjoy, or appreciate these delayed benefits in their very old age.
I still believe (in my situation anyway) in taking what you've earned and contributed while you can, and enjoy and use the money. Why let Uncle Sam keep your lifelong contributions until you're feeble, and if you pass away before break even (or even starting it at 70), never realizing your benefits?
This thread seems to have morphed. The first post said "I'll assume SS retirement dates are actuarially equivalent, but here's an interesting FIT angle". This post seems to say they aren't equivalent.
But, since I had a worksheet, I dug it out. Here are some numbers.
Assume I'm married, trying to get $50k of annual gross income from some combination of ordinary income (IRA, pension) and Social Security. We've got $21k of SS if we start at 62 and $28k if we start at 66.
If we start at 62, we'll need $29k of non-SS income to get up to $50k.
Only $3,750 of our SS will be taxable, so our AGI is $32,750.
Assuming standard deduction, we've got $12,950 of taxable income, our marginal bracket is 10%, and our FIT is $1,295.
If we defer to 66, then in the four years prior to 66 we'll need $50k of non-SS income.
That generates $50,000 of AGI,
$30,200 of taxable income,
a marginal bracket of 15%, and a FIT is $3,638.
After the first four years, we'll need $22k of non-SS income.
Only $2,000 of the SS is taxable, for an AGI of $24,000,
taxable income of $4,200,
and FIT of $420.
If I did all those numbers correctly (no guarantees) in the start-at-62 scenario we'll pay $1,295 every year. In the defer-to-66 we'll pay $3,638 for four years, and $420 thereafter.
I won't claim that one is clearly better than the other.
Note, however, that this ignores the fact that the $32k and $44k trigger points aren't inflation indexed. So taxes in all cases go up as inflation shrinks those numbers. That's an additional complication.
I was targeting a higher income than $50k. After looking at various scenarios, I thought there were too many variables to predict with much accuracy.