Calendar Day Calculation Across Years

From 1988 to 1995: total 7 years. Leap years in this period passing Feb 29: 1992 (since 1988 Feb 29 is before April 23, 1988, leap day of 1988 is counted if going forward from April 1988? April 23 1988 to April 23 1995 contains leap days 1992). Total odd days = $7 \times 1 + 1 = 8 \equiv 1$ odd day. So 23rd April 1995 is 1 day ahead of 23rd April 1988. Since 23rd April 1995 is Tuesday, 23rd April 1988 was Monday.