Dates / Date Arithmetic
Date Arithmetic
Add and subtract days to find future and past dates. Calculate days between two dates. Grades 3–4.
➕
Add Days
Start date + N days = future date
➖
Subtract Days
Start date − N days = past date
📏
Days Between
Date A to Date B = ? days
Strategy: Count in Chunks
When adding many days, count in chunks of 7 (weeks) first, then add remaining days. This is faster than counting one day at a time.
Example: March 5 + 25 days = ?
- 25 days = 3 weeks + 4 days (25 ÷ 7 = 3 remainder 4)
- March 5 + 3 weeks = March 26
- March 26 + 4 days = March 30
- Answer: March 30
Crossing Month Boundaries
When adding days takes you past the end of a month, you need to know how many days are in the current month.
Example: January 28 + 10 days = ?
- January has 31 days. Jan 28 → Jan 31 = 3 more days in January
- 10 − 3 = 7 days remaining, now in February
- Answer: February 7
Counting Days Between Two Dates
Use the jump method: count to the end of the start month → count full months → count to the target date.
March 15 → May 3
Mar 15 → Mar 31 = 16 days
Apr 1 → Apr 30 = 30 days
May 1 → May 3 = 3 days
Total: 16 + 30 + 3 = 49 days
Practice Drills
20
Example: 4 × 2