I find it impossible to make exact plans for contingency, other than to leave a lot of headroom for the unanticipated.
I started running Quicken only in mid 2010, hence only have accurate data for the four years of 2011 through 2014, but always have a rough idea of what the recurrent charges are. It is always the lumpy "one-time" charges that add up. But then, perhaps it's because of the available headroom that I allow myself to spend.
In the past 4 years that I have accurate data, 2011 was my biggest year: younger son still in school, and us helping daughter with a big down payment on a house. But I still had part-time income, so we did not at all hesitate with our generosity. And our expenses were higher still in earlier years, but I did not have the category breakdown.
My daughter's home has appreciated to 180% of what she paid, so we felt pretty good. If nothing else, I hope we showed her the advantage of having savings, read cash on hand, to buy things on sale, whether it's real estate or stocks.
The next year, 2012, saw my expenses dropping to 73% of 2011, and I started to think that my worry would be too much money I would not know how to spend. Ha!
My expenses then climbed back up, and were 22% higher in 2014 than that low year of 2012. It is still significantly lower than 2011, however. And my stash has grown too, but I cannot count on that every year.
So, my plan in retirement is still the same as when we were working. Leave plenty of headroom relative to what we think we need, because we will always manage to use it up.