I use an Excel spreadsheet and update it a couple times each month. Less than 1% of our spending is cash, so I don't worry about where it went and just record ATM withdrawals in the cash line. Credit cards and checking account bill pay make it easy to reconcile everything - that and neither of us are spenders. I tried Mint, but I didnt like it and went back to Excel.
Sounds pretty similar to us. We too have settled on an Excel spreadsheet (or 2 or 3 or 4)
1) A macro-view of savings, investments, pension savings (updated once per month, takes 1/2 hour or so)
2) A what we spent on everything over the last 5 years (it really does help doing almost all spending via cards, takes about an hour per month at most once back-track was complete)
3) A forward projection assuming a not yet FIRE (i.e. one or both of us keep working)
4) A forward projection post-FIRE assuming a dynamically-specified future FIRE date
I have been maintaining (1) for more than 10 years
(In fact back to 2001 when we were theoretically capable of finishing paying our mortgage
and we have thus been saving / investing over 50% of earnings ever since.)
My spouse started maintaining (2) starting just over 2 years ago and we back-tracked over the previous 3 years bank statements and credit card statements.
You'd be amazed how quickly past expenses end up being categorized as "miscellaneous" if you don't track the spending promptly.
Our "misc" category went way down when we tracked the spending each month.
In the last 12 months we have both been working on (3) and (4) to firm-up on a realistic FIRE date based on a SWR of 3% over a 40+ year retirement
based on a cost-of-living-adjusted annual spending derived as an average over the last 5 years
(which included a pretty representative collection of "one-off" spends).
We were looking at sometime *before* May 2015, ideally in April 2015,
but the little "wrinkle" of my being made redundant / laid-off a little over a week ago might push that target out a little,
but probably not by much because my spouse is still working and earning more than our expenses.