Let’s put some numbers to this. I’ll use $15,000 at age 62 and $20,000 at age 66. To keep it simple, I’ll assume one lump sum at the end of the year.
First let’s do the break-even point for money received. If you start collecting $15k per year at 62, in 16 years, at age 78, you will have collected $240,000. If you get $20k annually at 66, in 12 years, at age 78, you will have received $240,000. So, the break-even point is 78 years old (which is really age 79 if you consider the payments a lump sum at the end of each year).
Let’s do it another way (which is why I love math, you can do problems multiple ways and get the same result). Collecting $15k at age 62 will give you $60,000 by the time you hit age 66. Subtracting $5,000 from that per year will make it last 12 more years, until age 78.
Opportunity Cost
Idle money can make money by putting it in investments. I’m not sure what interest rates you can find at the moment, but I know I’m paying 4% on a car loan and I know people that are paying less. So, unless you put your money into risky investments, you won’t get that rate.
Let’s say you can get a 2% annual return.
Starting to collect at age 62, you’ll have $60,000 at age 66, plus the interest you’ve collected on the money. That’s 2% on $15k for 4 years, another 2% on $15k for 3 years, etc., plus interest on the interest. So after 4 years, with interest you’ll have $63,060 ($3060 is interest).
Now, to equal the $20k you would have gotten if you waited until age 66, take $5,000 out of your bank every year, and add the interest to the remainder. So, ($63,060 – $5000) *1.02 = $59,221 left in the bank at age 67. I’m sure there is some calculusy way to figure this out using integrals and limits and other such nonsense, but you can also brute force it (which is the method I used). It comes out by age 80, you have $1,740 left in your bank.
So, investing your money at 2% interest will push the break-even point out another 2 and a third years, to 80⅓.
COLA
A few posters mentioned COLA, which I assume stands for Cost of Living Adjustment. So I will throw that into the mix.
If you start collecting early, you’ll get the COLA on the $15,000, but not on the extra $5,000 that would get the COLA if you started collecting at age 66. So, to add that into the equation, instead of withdrawing $5,000 each year after age 66, withdraw the COLA adjusted amount. For example, if the COLA rate were 1%, subtract $5,203 from the first year (4 years of COLA), $5,255 the second year, etc.
I didn’t do the calculations, but it should make the break-even point land somewhere between 78 and 80.
Other posters have listed all the other advantages and disadvantages that I can think of. If you want to be on the safe side, wait to start collecting if you have the choice. If you kick off early, you won’t have to live with the mistake you made.