Is there something somewhere on the board that would calculate retirement costs, sort of like the buyout calculator?

There isn’t a cap hit associated with retiring, unless the player is on a back-diving contract that is now illegal. For those contracts you can easily find the cost by doing a quick google search.

In normal circumstances, retirement is essentially the same as terminating the contract. (It comes off the books, and the team stops paying the player)

I was specifically wondering for Jack Johnson who has a partially dropping contract. $3.25 hit; $4, $4, $3, $3, $2.25 salaries. He has been paid $8M over 2 years. From what I saw in the CBA it appears that you compare that $8M vs $6.5M (3.25x2), $1.5M difference, 3 years left... $500K hit per year. But I wasn't sure if that was right.

If he outright retires, the cap hit comes off the books as the team will no longer be paying him.

Not that straight forward according to the CBA.

Cap Recapture Penalty

Article 50.5 -Upon that Player’s failure to play in the League by reason of retirement, “defection” from the NHL or otherwise (but not death) (such that he is not playing and is not receiving Salary pursuant to his Long-Term Contract) (assuming it is prior to the conclusion of the Long-Term Contract), the difference between the sum of the Actual Salary and Bonuses received by that Player under that SPC and the sum of the Averaged Amounts charged against the Club’s Averaged Club Salary under that SPC shall be calculated as follows:

(i) First, calculate the total Actual Salary and Bonuses paid to that Player under that SPC (“Total Payment”) until the date of such retirement, defection or otherwise (but not death);

(ii) Second, calculate the total Averaged Amount charged against the Club’s Averaged Club Salary for the Player under that SPC (“Total Cap Charge”) until the date of such retirement, defection or otherwise (but not death);

(iii) Subtract Total Cap Charge from Total Payment. That number shall be referred to as the “Cap Advantage Recapture.”

(iv) The Cap Advantage Recapture shall be charged against the Club’s Averaged Club Salary in equal proportions in each League Year over the remaining term of the SPC (i.e., the yearly charge shall be calculated by dividing the Cap Advantage Recapture by the number of seasons remaining under that SPC).

That's what I did a couple posts up "$8M vs $6.5M (3.25x2), $1.5M difference, 3 years left... $500K hit per year." I just wan't sure.

I thought if you are over a certain age (35) the cap hit stays on the book?

That’s if you’re bought out, if you outright retire, then you’re obviously not paid anymore

Lots of different items in this post
Players that sign contracts after the age of 35 cannot have their contracts bought out without a team retaining the full cap for the life on the contract
Players that retire.....no further cap implications for the team. But the cap implications happen if the contract was front loaded. Then a team(s) that get the paid extras money over the cap hit get hit with a recapture penalty. Louango retired as a Panther but because the his years as a Canucks with a front loaded contract the Canucks are responsibe for recapture.
There isn't really "LTIR retired " It's LTIR.