If you're past your FRA and not currently taking retirement benefits, Social Security's estimate of your current retirement benefit will include delayed retirement credits (DRCs). In order to adjust this to your retirement benefit at your FRA, these DRCs need to be backed out of your current estimate. There are other adjustments the Social Security Administration makes to your estimate, including adjustments due to continued income, but for our calculations to be accurate, the only adjustments you need to worry about are the DRCs — we'll take care of the rest.

The monthly DRC increase is 2/3 of 1% = 0.08 / 12 = 0.0067.

To remove the DRCs from an estimate, you need to divide the estimate by (1 + (number of months past FRA the estimate is from) * 0.0067).

For example, if a retirement benefit is for $2,500 and is from 23 months after FRA:

$2,500 / (1 + (23 * 0.0067)) = $2,500 / 1.154 = $2,166.

If the amount is from exactly 1, 2 or 3 years after FRA, you can substitute years for month. So if the above example was from 24 after FRA:

$2,500 / (1 + (2 * 0.08)) = $2,500 / 1.16 = $2,155.