[zcvosdfdgj]

No, he definitely means the following day. He continues:

If by next Thursday you still haven't paid, then that 10% turns into 20%. If you leave it for a month, congratulations, your invoice is now 150% of the original.

4 weeks in a month.. so:

day 1: 10% day 7: 20% .. day 30: 50%

It only works if he charges 10% the very first day it is late.

[Tyrannosaurs]

That's what each week or part thereof means - you pay for each week and partial weeks are rounded up to whole weeks (so one day = one week, one week and one day = two weeks, one month is four weeks and two days so would be five weeks and so on).

[zcvosdfdgj]

ok... that makes sense.

[Avenger42]

No, day 7 is still 10%. Day 8, it bumps up to 20%.