Retirement plot and table calculations are inconsistent and calculator rounds savings rate to nearest 2% before proceeding about networthify

[ragibson]

I thought about this a bit more and put a bit of a re-imagined version at https://ryanagibson.com/posts/analytic-early-retirement-calculator/ -- other than Networthify's rounding, the impact seems to usually be limited to a year or so.

That said, the absolute impact from rounding is especially bad at the lower end if anyone were to try to use it for more typical retirement planning (where I'm pretty sure the usual consensus is a minimum target of ~10%). For relative error, it would be worst for users very close to retirement.