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Date Calculation in Scratch - Adding Days and Converting Formats

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DP

DateCalc_Pro

Posted on July 29, 2025 • Intermediate

📚 Library System Date Calculation Help

I’m building a library checkout system in Scratch and I need to calculate return dates. When someone checks out a book, I want to automatically calculate the date 75 days from today and display it in a nice format.

For example:

  • If today is August 1st, the return date should be around November 15th
  • I need it formatted as “Month Day, Year” (like “November 15, 2025”)
  • It should handle month boundaries and leap years correctly

I’ve been struggling with the math for converting days across months. Does anyone know how to do this properly in Scratch? 🤔

AM

AlgorithmMaster_Jake

Replied 2 hours later • ⭐ Best Answer

Great question @DateCalc_Pro! Date calculation is tricky but totally doable in Scratch. Here’s a complete solution for your library system:

📅 Date Calculation Flow

Here’s how we’ll approach the date calculation:

flowchart TD A[📅 Current Date] --> B[Convert to Days Since Reference] B --> C[Add 75 Days] C --> D[Convert Back to Date] D --> E[Format as Month Day, Year] F[🗓️ Date Components] --> G[Year] F --> H[Month] F --> I[Day] G --> J[Handle Leap Years] H --> K[Days in Each Month] I --> L[Day of Month] J --> M[📊 Final Calculation] K --> M L --> M style A fill:#e1f5fe style E fill:#e8f5e8 style F fill:#fff3e0 style M fill:#f3e5f5

🔢 Step 1: Set Up Date Variables

First, create variables to store date information:

    when flag clicked
// Current date variables
set [current year v] to [2025]
set [current month v] to [8]  // August
set [current day v] to [1]

// Days in each month (non-leap year)
set [days in months v] to [31,28,31,30,31,30,31,31,30,31,30,31]

// Month names for formatting
set [month names v] to [January,February,March,April,May,June,July,August,September,October,November,December]

📊 Step 2: Convert Date to Days Since Reference

Convert the current date to total days since a reference point (like year 2000):

    define convert date to days (year) (month) (day)
// Calculate days from years
set [total days v] to (((year) - [2000]) * [365])

// Add leap days
set [leap years v] to [0]
set [check year v] to [2000]
repeat until <(check year) = (year)>
change [check year v] by [1]
if <(is leap year (check year)) = [true]> then
change [leap years v] by [1]
end
end
change [total days v] by (leap years)

// Add days from months in current year
set [month counter v] to [1]
repeat until <(month counter) = (month)>
if <(month counter) = [2]> then
if <(is leap year (year)) = [true]> then
change [total days v] by [29]
else
change [total days v] by [28]
end
else
change [total days v] by (item (month counter) of [days in months v])
end
change [month counter v] by [1]
end

// Add remaining days
change [total days v] by (day)

🗓️ Step 3: Check for Leap Years

Create a function to determine if a year is a leap year:

    define is leap year (year)
if <<((year) mod [4]) = [0]> and <not <((year) mod [100]) = [0]>>> then
set [leap year result v] to [true]
else
if <((year) mod [400]) = [0]> then
set [leap year result v] to [true]
else
set [leap year result v] to [false]
end
end

➕ Step 4: Add Days and Convert Back

Add 75 days and convert back to a readable date:

    define add days to date (days to add)
// Convert current date to total days
convert date to days (current year) (current month) (current day)

// Add the specified days
change [total days v] by (days to add)

// Convert back to year/month/day
convert days to date (total days)

// The result will be in [result year], [result month], [result day]
  
    define convert days to date (total days)
set [remaining days v] to (total days)
set [result year v] to [2000]

// Find the year
forever
if <(is leap year (result year)) = [true]> then
set [days in year v] to [366]
else
set [days in year v] to [365]
end

if <(remaining days) > (days in year)> then
change [remaining days v] by ((-1) * (days in year))
change [result year v] by [1]
else
stop [this script v]
end
end

// Find the month
set [result month v] to [1]
forever
if <(result month) = [2]> then
if <(is leap year (result year)) = [true]> then
set [days in current month v] to [29]
else
set [days in current month v] to [28]
end
else
set [days in current month v] to (item (result month) of [days in months v])
end

if <(remaining days) > (days in current month)> then
change [remaining days v] by ((-1) * (days in current month))
change [result month v] by [1]
else
set [result day v] to (remaining days)
stop [this script v]
end
end

📝 Step 5: Format the Date

Create a nicely formatted date string:

    define format date (year) (month) (day)
set [month name v] to (item (month) of [month names v])
set [formatted date v] to (join (join (join (month name) [ ]) (day)) (join [, ] (year)))

// Example output: November 15, 2025

🎯 Step 6: Put It All Together

Here’s how to use everything for your library system:

    when [checkout book v] clicked
// Get current date (you might get this from sensing blocks or user input)
set [current year v] to [2025]
set [current month v] to [8]
set [current day v] to [1]

// Calculate return date (75 days later)
add days to date [75]

// Format the result
format date (result year) (result month) (result day)

// Display to user
say (join [Return by: ] (formatted date)) for [3] seconds

// You could also set this to a variable for storage
set [book return date v] to (formatted date)

🚀 Advanced Features

You can extend this system with additional features:

Get Current Date Automatically:

    when flag clicked
// Get current date from sensing
set [current date string v] to (current [date v])
// Parse the date string to extract year, month, day
// This depends on your locale format

Different Loan Periods:

    define calculate return date (book type)
if <(book type) = [regular]> then
add days to date [14]  // 2 weeks
else
if <(book type) = [reference]> then
add days to date [7]   // 1 week
else
add days to date [75]  // Special collection
end
end

Overdue Calculation:

    define days overdue (return year) (return month) (return day)
convert date to days (current year) (current month) (current day)
set [current total days v] to (total days)

convert date to days (return year) (return month) (return day)
set [return total days v] to (total days)

set [overdue days v] to ((current total days) - (return total days))

This system handles leap years, month boundaries, and gives you a solid foundation for any date-related calculations in your library system! 📚✨

DP

DateCalc_Pro

Replied 1 hour later

@AlgorithmMaster_Jake This is exactly what I needed! 🎉 The step-by-step breakdown makes it so much easier to understand.

I implemented it in my library system and it works perfectly. The leap year handling was the part I was missing. Thank you!

MT

MathTeacher_Lisa

Replied 45 minutes later

Excellent explanation @AlgorithmMaster_Jake! 👏 This is a great example of breaking down a complex problem into manageable steps.

For students learning this concept, I’d recommend:

  • Start simple: Try adding just a few days first
  • Test edge cases: End of month, end of year, leap years
  • Use debugging: Add “say” blocks to see intermediate calculations
  • Understand the math: Learn why leap years exist and how they work

This kind of algorithm thinking is valuable beyond just Scratch! 🧮

VB

Vibelf_Community

Pinned Message • Moderator

🧮 Master Advanced Math and Algorithms

Great discussion about date calculations! For those interested in learning more advanced mathematical concepts in programming:

  • 📅 Calendar algorithms and date arithmetic
  • 🔢 Number theory and modular arithmetic
  • ⏰ Time zone calculations and conversions
  • 📊 Statistical calculations and data analysis

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