Last month of job in resumee

I always struggle with which month put as the last I've worked in a position, current month or the next one.
For example, assume someone ended a job October 15. What would yo put as the end month, October or November? Assuming a common format of using the month and the year, but not the day of the month.
Someone may consider an end date of October as "worked up to September 30", but others might consider October as worked up to "October 31".
What do you do?
For example, assume someone ended a job October 15. What would yo put as the end month, October or November? Assuming a common format of using the month and the year, but not the day of the month.
Someone may consider an end date of October as "worked up to September 30", but others might consider October as worked up to "October 31".
What do you do?
Comments
If they checked and you only worked until September 25, they could take that as dishonest and end discussion.
2015 Start WGU (Feb) Net+ (Feb) Sec+ (Mar) Project+ (Apr) Other WGU (Jun) CCENT (Jul) CCNA (Aug) CCNA Security (Aug) MCP 2012 (Sep) MCSA 2012 (Oct) Linux+ (Nov) Capstone/BS (Nov) VCP6-DCV (Dec) ITILF (Dec)
2015 Start WGU (Feb) Net+ (Feb) Sec+ (Mar) Project+ (Apr) Other WGU (Jun) CCENT (Jul) CCNA (Aug) CCNA Security (Aug) MCP 2012 (Sep) MCSA 2012 (Oct) Linux+ (Nov) Capstone/BS (Nov) VCP6-DCV (Dec) ITILF (Dec)
Assume a job from Sep 1 to Oct 31. If in a English job site (or LinkedIn) you put Sep - Oct, it will say 2 months. However, if you put the same on a Spanish job site, it says just 1 month.
2015 Start WGU (Feb) Net+ (Feb) Sec+ (Mar) Project+ (Apr) Other WGU (Jun) CCENT (Jul) CCNA (Aug) CCNA Security (Aug) MCP 2012 (Sep) MCSA 2012 (Oct) Linux+ (Nov) Capstone/BS (Nov) VCP6-DCV (Dec) ITILF (Dec)