$200K DateTime Bug: What Every Dev Gets Wrong About Time in Trading Systems

Precision issues with different DateTime types

It was 2:15 PM [ Friday afternoon], and the trading floor was humming with energy. Stocks were flying, orders were coming, and our systems were working overtime to keep up. Everything was smooth until it wasn’t. A confused trader called our client’s customer care, exclaiming, “Why are yesterday’s trades showing up as settled today?” as soon as we got this news we ran for a quick meeting…

By the time we uncovered the issue, it had already cost us $200K in delayed settlements and botched order executions..

The culprit? A simple but DateTime bug hidden in our code….

— Problem

If you think time is straightforward, you probably haven’t worked on a trading system. For most applications, a timestamp is just a way to mark when something happened. In trading, time isn’t just important — it’s everything. Every millisecond can mean the difference between profit and loss. Here’s what we learned the hard way about the dangers of mishandling time.

1. TimeZone Handling

Our first mistake was assuming everyone in the world was operating in the same time zone(lol he was junior and its…