Last day is not important.

Last day of your period doesn't matter when determining most fertile days.

Get a copy of "Taking Charge of your Fertility."

Agree that first day is most important.
Also, the best information you can get about when you are most fertile is actually backwards-looking. which is really unhelpful for the first few months you are tracking, but then you can see your pattern. generally speaking, the first "half" of your cycle, from day 1 to ovulation, can vary widely from woman to woman. but the second half, from ovulation to your period, is almost always 12-14 days. so count backwards from day 1 to affirm when your most fertile days were last cycle. if you have a 35 day cycle, you're probably ovulating on day 21. if you have a 28 day cycle, you're ovulating on day 14. and so on.

Anonymous wrote:I'm not sure what the last day of your period has to with your fertile days. What are you trying to figure out related to your last day?

I count my last day when flow is gone. Sometimes there's a bit of brown spotting the following morning, I guess.

This. It's not the last day that matters, but the first day.

I'm not sure what the last day of your period has to with your fertile days. What are you trying to figure out related to your last day?

I count my last day when flow is gone. Sometimes there's a bit of brown spotting the following morning, I guess.

I'm trying to calculate my most fertile days, but I'm having difficulty determining when the last day of my period is. Is it the day when you see no spotting at all or when the flow is significantly reduced/almost gone? Even after my flow has stopped significantly, I still see very faint spotting. But I would consider my period was over before that.