I have tried 2 schengen calculators now and both return the same result.
At the end of my trip this September I will have zero days left due to previous trips the first of which was for 31 days. Both calculators show the zero figure until the 19th Oct when the days left jump to 31. Surely as the 180 day window rolls forward the allowance should increase 1 day at a time as the previous stay drops out of the 180 day window a day at a time. The calculators seem to be waiting until the end day of the previous trip before increasing the allowance, or am I missing something?
Thanks
Dennis

You could help by telling us which calculators you have tried......

Try this one it performs Rolling Window calculations:

www.ninety180.com


Steve

What is the official way of counting days? If you fly in and stay overnight is that two days or one?

I can't remember which country I was doing research on but their rule was quite precise by stating that if you are physically present there at 11:59pm then that counts as a day spent there. Does anyone know how this works in Spain/EU?

That is the correct way everywhere in the world (or should be depending on the attitude of the person behind the desk when you hand over your passport.) You will note that no stamp in the passport has a time just the date, therefore that is the deciding factor.
Arrive on the 22nd July 2025 at anytime from 00:00 to 23:59 and thats the day you got here.
I made the mistake of thinking that my 20 day work visa for Canada meant I could arrive in the afternoon of day one and depart 20 days later.
Nope I was questioned at length over why I was 6 hours over my visa as the first day started at 00:00 even though I didnt arrive until 20:00. Again no time on the visa when I loked after just a from to date (my flight was on the 21st day at 06:00)

This question arose a while ago as someone on here (or the other one we all post on) wanted to work the system. It was found that 'a day' is counted even if you arrive at 23:59 (if the officials were feeling nasty it would be time the plane/boat etc landed/docked) and not the time you passed out of border control.

Just found this

​​​​​​For visa purposes, a "day" is generally considered any 24-hour period where a foreign national is physically present in the country, regardless of the time of day they arrive or depart. Essentially, if you enter the country on a specific date, that date is counted as one day, even if you arrive late in the evening. Similarly, if you depart on a specific date, that date is also counted as a day. There are some exceptions, such as for transit passengers or those with a medical condition preventing departure.

That would be particularly nasty. I also wonder whether officials change the date stamp precisely at midnight or whether they wait until the line is cleared before spending a free moment doing so.

What's also worth looking into - albeit not pertinent in the OP's case - is that there can be a distinction between the way a "day" is treated for immigration and tax purposes. For the former it could well mean part of any day is treated as the full day (the aforementioned 11:59pm example), whereas the latter tends to look at it more sensibly and can be more compared to the number of nights spent somewhere.

Thanks Steve
That one works as I would expect it to.
The two i tried are "Schengel Cal" and "90 days schengen " Both from Google play store

Here it says "For the purposes of implementing paragraph 1, the date of entry shall be considered as the first day of stay on the territory of the Member States and the date of exit shall be considered as the last day of stay on the territory of the Member States."

Thanks, that pretty much sums it up. So a 7-night trip would be treated as spending 8 days in the Schengen zone.