Help me understad this please!

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When you say "week 6" in US, do you mean 5+0 days - 5+6 OR do you mean 6+0 unti 6+6 days?
In europe we count full weeks, mening when you are 5+ days, we say you are in weeks 6 and so on. 
Please let me know how you count 🙏🏼🙏🏼🙏🏼🙏🏼