Here's my recent history (a couple of years worth). As you can see I'm using between 1 and 1-1/2 mg per day since I switched to 66 mg/ml nicotine. I upgraded from my original (not recorded here) 36 mg/ml to stop chain vaping. I actually had to rotate three rigs to prevent them from getting so hot that they cooked the juice and burned my lips and fingers. Once I switched to a higher (50 mg/ml and others) I dropped from around 5 ml/day (i've never enjoyed cloud chasing) to much lower levels; I also discovered that I was using LESS nicotine even though I was using stronger e-juice.
I experimented with much stronger e-juice (100 mg/ml or 10% nicotine) but found that it was all too easy to "over-puff" and make myself slightly nic-sick. Dropping back to the 66 mg/ml was still enough to keep me from chain-vaping and dropped my daily use of nicotine to under 100 mg of nicotine per day, so that's where I've continued to mix my e-juice. Totally unflavored.
I mix either 180 or 360 ml of juice at a time, and record when I refill my two 30 ml dispensing bottles (those 60 ml in column 2). There is sometimes a bit less than the full 60 ml left in my mixing jar which accounts for the occasional odd number in column 2. A bit of calculation gets me the number of days to use that amount, and the ml/day and mg/day numbers. I pre-fill the strength column since that rarely changes.
I may switch to refilling and recording only one dispensing bottle at a time, which would give me a bit more granularity in my records. It's not like doing a refill every two or three weeks would be too much effort.
(to read the last column: 0.050 = 5% or 50 mg/ml nicotine; 0.066 = 6.6% or 66 mg/ml)