Spreadsheet Errors, Mistakes and Horror Stories

Spreadsheets have been the original no-code tool since the dawn of personal computing. They have seen widespread use for tasks varying from personal accounting, to-do lists and keeping game scores to genetics, machine part cataloging, game development, AI research, creating reports, and performing data analysis. They are used by small businesses and mega corporations alike. The flexibility of spreadsheets and their ad-hoc nature allows users to quickly start a new project or adapt an existing one to new requirements. This is why spreadsheets remain a popular choice, despite the wide variety of specialized tools and spreadsheet replacement wannabes developed throughout the years.
However, flexibility comes at a cost. The user interface of the spreadsheets and the lack of implicit structure contribute to increased chance of making mistakes. Copy-paste errors, inconsistent formulas, incomplete data ranges, incorrect format, data disclosure due to hidden data, etc. are common occurrences in many a spreadsheet.
Below are some or the most high-profile publicly known spreadsheet errors, background that lead to their occurrence and the implications in the real world. Studying the mistakes of the past can help us to do better in the future.

Babylonian Educator Makes a Data Entry Mistake in an Answer Key Table

In what constitutes the known oldest spreadsheet bluder, a Babylonian Educator enters incorrect data in answer key table for trigonometry exercies.

Boeing Discloses Personal Information Through Hidden Spreadsheet Cells

Boeing employee mistakenly emails spreadsheet full of employee personal data to his spouse, but risk of harm is declared to be low.

Columbia Housing Authority Alleges Overpayment for Section 8

An unspecified Excel spreadsheet error leads to incorrect 'over-housing' of tenants and larger than appropriate vouchers issued to landlords.

Crypto.com Refunds the Amount of $10.5 Million Instead of Just $100

Excel data entry error and lack of validation rules leads to couple splurging on 4 houses, gifts, vehicles and more, with $4M to spare.

England's PHE Undercounts COVID Cases Due to Import to Excel Bug

Usage of Excel as a database, old XLS format and lack of error handling leads to temporary undercounting of COVID cases.

Eskom Mine Inflates Fine by R1.5bn Due to Spreadsheet Error

Error in a spreadsheet leads to underestimation of coal quality and overestimation of amount of fine to be paid.

Kodak Spreadsheet Mistake Causes Incorrect Accrual, Restating Loss

Faulty spreadsheet leads to incorrect calculation of $9 Million severance pay, leading to incorrect losses report.

London Olympics Oversold Tickets Due to a Spreadsheet Mishap

Lack of spreadsheet input validation and incorrect input lead to over-selling of seats for 2012 London Olympics swimming competitions.

Mouchel Blames £4.3m of £8.6m Writedown on a Spreadsheet Bug

A spreadsheet error is blamed for incorrect calculation of pension fund deficit, doubling losses a day before profit warning.

The Luxembourg Ministry of Housing Publishes Incorrect Spreadsheet

As part of a reform of property taxes the ministry published an Excel spreadsheet to assist rent calculation. The initial version contained a formula error.

Westpac releases profit numbers prematurely in a spreadsheet

Incorrectly releasing a spreadsheet template instead of offical data leads to stopping trading of shares of Australia's oldest bank.

The same stories are also available sorted by year.