Days 1-3: Hanoi
Three nights give you time to recover from the international flight and see the capital without rushing. Split the city into the old centre, a history/culture day, and a flexible day for food and neighbourhoods. Do not put a long excursion first thing after arrival.
Days 4-5: Ninh Binh or a northern bay
Choose one large nature block. Ninh Binh is easier logistically and gives you rivers, karst landscapes, and temples. A bay cruise is a different experience but requires its own organisation. You can technically do both in two weeks, but leaving room to rest usually produces a better trip.
Day 6: Central Vietnam
Fly to Da Nang and treat this as a transport day: airport transfer, check-in, flight, baggage, onward transfer, and hotel check-in. A good dinner in the evening is already enough.
Days 7-10: Da Nang, Hoi An and Hue
You can base yourself in one place and travel around. Hoi An does not require a hotel change if you stay in Da Nang; Da Nang does not require a separate night if you prefer Hoi An. Keep at least one day without a long transfer.
Day 11: Ho Chi Minh City
Fly south and keep the evening easy. After more compact destinations, central Ho Chi Minh City feels completely different: and that contrast is the point of a three-region itinerary.
Days 12-13: Ho Chi Minh City
Use one day for the city itself. On the second, either go deeper into the city or take a Mekong Delta day trip. Do not treat the Mekong as a mandatory checkbox if, after eleven days of travel, the last thing you want is another bus.
Day 14: Buffer
Spend the final night in your international-departure city. That way, a delayed domestic flight does not turn into a missed long-haul ticket.
If you want more beach time
Do not add Phu Quoc on top of this itinerary. Remove Ho Chi Minh City or the northern nature block and give the freed three or four days to a beach destination. Two weeks is enough for variety but not for a good-quality holiday in five regions.
Questions and answers
Can I see both northern and southern Vietnam in two weeks?
Yes, if you use domestic flights and limit yourself to three regional bases.
Should I add Phu Quoc?
Only instead of another itinerary block, not as a fourth region on top of an already full trip.
How many days do I need in Hanoi?
For a first visit, two or three full days gives you a good introduction without rushing.
Do I need an overnight train?
No. Use one because the experience or the route suits you, not because it is supposedly 'more authentic'.