even as a youngun' I thought the 80% of income was a dumb estimate.....My net was never 80% of gross even then....now, after the government gets its cut and I pay for insurance (life, health, disability), and EI (unemployment insurance ), CPP (Canadian Pension plan - so I guess force d savings), I get to 'keep' just less than 60% of my pay.....
I've used those calculators, but I always put in a fake salary that had the 80% come out to be the number I wanted my spend to be.
But I am amazed at how many people out in the 'real world' don't have a clue what their yearly spend is. I don't track my expenses as closely as some here, and my buckets are rough (ie if I bought it in a grocery - it's grocery even if it was laundry soap, if I bought it at walmart it's home even if it was bread)....95% of our spending is via credit cards, so I just down load the transactions each month, dump them into rough buckets based on 'where' and track that way. I spend maybe 10 minutes a month doing this, and I have over 5 years of expenses tracked that way....I add in the one-offs or yearly costs and it gives me a pretty good idea of what our spend will be....and my retirement budget has a generous (for me) travel line item, if the market is off or we have an unexpected cost, we don't travel that year.