The spreadsheet seems to be working fine for me. I bought a nice road bike this month, so savings weren't quite what they would have been, but I got a hell of a deal on the bike. Used on Craigslist for $1,000, the MSRP is $4,200, has all the components I would like and came with clipless pedals and a pair of shoes.
Oct: $70,999.50
Nov: $73,869.62
Saved: $2,870.12
Next month our new high deductible health plan starts taking premiums, which will mean a bit of savings for us along with the adjustment done on my W-4, we should see our savings accelerate.