No calculation is 100% accurate.
To determine the most accurate Maintenance calorie number, you have to do a little experimenting.
The best way to figure out if your Maintenance number is accurate, weigh yourself first thing every morning for a week.
You then take your weight from all 7 days, add them, and then divide them by 7 which will give you the average and let you if you stayed the same, or you lost weight.
Do this for 4 weeks.