Why does "every eight days" mean once a week?

Mi amigo Bert, who grew up in Mexico, told me last night that he's never understood why the expression "cada ocho dias" (every 8 days) means once a week. My theory is that if you "count both ends" (such as Friday == 1, Saturday == 2, etc.) the next week (Friday in this case) is #8.

Am I on the right track, or have I gone off the rails?

• Note: the same thing happens with quincenal (every 15 days), meaning once a fortnight. Commented May 18, 2018 at 10:00
• I'm voting to close this question as off-topic because it's not about Spanish language itself. Commented May 18, 2018 at 18:30
• @FGSUZ - I think it's a good question. I see your point about the cultural usage aspect, but I think it intersects enough with language and usage to make it useful for the site. Commented May 19, 2018 at 14:08
• This is a great spanish question about uses and costumes
– Mike
Commented May 23, 2018 at 15:32

1 Answer

Yes, you include "Today", and refer to the same day next week.

If today is Monday then:

``````Today:1
Tuesday:2
Wednesday:3
Thursday:4
Friday:5
Saturday:6
Sunday:7
Monday:8
``````

This is very common in Spanish, and also interchangeable for 7 days.

Everyone will know you meant next week.

Mathematically speaking it would be 7 days, since from today to next week same day there is only 168hr = 7days.

• Quizás dependa del país o región. Para mí una vez por semana es cada 7 días. En cuanto a un intervalo de tiempo yo incluiría siempre ambos extremos, por lo que 42-44 significa 3 versículos. Commented Jun 13, 2015 at 6:40
• I'm spanish and I haven't ever heard this expression. About the days range, here it is usual to count both starting and last day, but it is also habitual to specify that they are both included: de lunes a domingo, ambos incluidos Commented Jun 15, 2015 at 0:12
• @HéctorE I'm from Spain too and though I have never heard that exact idiom either, I've heard "[de] hoy en ocho", which means "next week, on the same weekday as today". I guess it's similar to using "15 días" to say two weeks. Commented Jun 15, 2015 at 9:21
• I'm from Colombia and have lived in Ecuador and visited many countries in Latin America. In my experience "de hoy en ocho" is normal, and frecuently used. Commented Jun 19, 2015 at 13:15
• In English we sometimes make the distinction between "to" when used between dates and "through." Technically, I believe that a dash means "to," but is often interpreted as "through." The word "through," of course, means that the day ending the range is counted. Nevertheless, a week-long conference beginning on Monday, the 1st and going through Friday, the 5th, would be written as (using May as an example) May 1st-5th (or May 1-5) and it would be assumed that the conference would also be in session on the 5th or final day. Commented Apr 23, 2017 at 0:46