How minutes are there in a year? Thanks to the solar system, it’s complicated, but Google tells us one answer: 525960. That’s equal to 8766 hours, or 365.25 24-hour days, which is the average number of minutes in a Julian calendar year. Google also gives a nice tip: in case 525960 is too long for you to remember, you can also use this approximation: 526000.
When you just want to do some quick mental math, there’s actually an even nicer approximation: 5e5, or 500000. “But 500000 is a much farther off than 526000”, you might say, and you’d be right. But 5e5, or five hundred thousand, is less to remember, and when the time comes that you need to compute a closer figure, you already roughly know the error: it’s actually pretty close to 5%. 5e5 times 1.05 is 525000, less than a day under the “true” value.
So remember this: 5e5 minutes is 5% off, add 960.