Perpetual calendar in the head

Today is Thrusday, April 10th, which day of the week is September 3rd? It is actually easy to calculate these things, without the computer's help:

As today is Thursday, 17th, 24th and 31st are also Thursdays. April has only 30 days, so 31st of April is actually May 1st (and it is a Thursday).

Continue with Thursdays: May 1st, 8th, 15th, 22nd, 29th, 36th. May 36th is (36 - 31) = 5th of June.

June 5th, 12th, 19th, 26th, 33rd [-30] = July 3rd, 10th, 17th, 24th, 31st, July 38th = August 7th, 14th, 21st, 28th, 35th, which is September 4th - those were all Thursdays, so September 3rd is a Wednesday.

To go faster we could add several weeks at a time - like 3 or 4 to not overshoot a month completely. 3 weeks (21 days) probably is easier to add, arithmetics-wise, than 28 days.

Let's check October 17th: September 3rd is Wednesday, so September 24th is, too and so is September 45th, which is October 15th. Therefore, October 17th is a Friday.