foyer and hallway 10 % seems accurate. Bigger rooms 5 to 7

Your husband is totally incorrect. Having enough flooring to do the job right isn't the place to cheap out. And you need to have extras to store in case of damage down the road.

10% extra is fine for ceramic or porcelain laid straight. 15% for a diagonal layout.

You're not doing ceramic or porcelain. For natural stone, 15% allows for you to be able to cull some of the less "pretty" tiles as well as enough to allow for cuts. 20% for natural stone on the diagonal.

For some stones with a wide variation like some slates, 20-40% would be needed because the cull rate is much higher. I've seen cheap slate from a box store that had a 2 out of 3 cull rate. That takes that "bargain" price to a much higher level if you have to account for the unusable stone.

I recently ordered 20 X 20 porcelain tile for my kitchen and powder room. Square footage was measured and 15% was added for overage as floor will be laid diagonally. Well.....tile was laid and installer ran out of tiles for the powder room. I had to order 2 additional boxes asap which we are waiting for. I posted this on the kitchen forum and I was told that 20-25% is overage is best for diagonal floor.

6-10 percent for an average tile job. A bit more if it is staggered joint or diagonal. Never should be more than 10%.

Actually, with extra large format tile, anything over 8 square feet per piece (24"x48") my experience is that 25-30% is closer to correct for the overage. Where a single tile is 8-10 square feet, 1 broken tile is a huge portion of a given area.