The shipping estimate on the USPS website is lovely, but its not actually guaranteed for most shipping classes. For First Class mail, estimating when it will ACTUALLY arrive vs when the the USPS says it will can be frustrating. Having shipped hundreds of packages overseas, here’s how I estimate when the overseas customer should be looking for it. This doesn’t guarantee this is when it will turn up… but it gives a narrower range than the 4-20 the USPS lists.
This is the estimate for First Class. Priority is usually a little faster, but not guaranteed. Start with one day. You’ll add days for where it originates from and where its going TO. If you don’t immediately recognize the destination, look it up on the internet. Keep in mind this is BUSINESS DAYS. Make this clear to the customer as well. Holidays don’t count as “days” for the estimate!