I've read many of the threads on this but felt one part doesn't really get discussed much. So perhaps I am missing something. Let's say you have 1.25 million in cash but have a mortgage of $250k paying $1350 a month on it. Your SWR is 4% which is $50,000 a year but you spend $16200 for the mortgage so you have $33800 to spend each year other than the mortgage (plus SS, any pension).
But you then pay the mortgage leaving $1 million. At a 4% SWR you then have $40000 to spend each year. Isn't that an argument in favor of paying the mortgage ...at least for those for whom the difference between $33800 and 40000 would be meaningful?
That's an annual difference of $6200.
If you use an SWR of 4.5%, the difference is $4950. But!!! Now the net income (after mortgage payments) is $40,040. That's essentially the same as $40k
If your portfolio is a bit bigger--$1.5M--, the 4%SWR difference is still $6200, but now the net income is $42,800. Bigger than $40K.
So, from one aspect, it all depends on your viewpoint.
Is $40K what you think you need?
Do you want to use a really low SWR? Or are you comfortable with a slightly higher SWR? Why did you pick 4%? Why not 3.9%? Or 3.5%?
Are you focussed on the absolute dollar delta?
If your need is less than $33,800, then there is no need to reach for $40K. It's overkill. How much do you want the rubble to bounce?
De gustibus non disputum.