So when ever I’m getting close to my arrival airport the ATC automatically tells me to reduce my altitude and I listen to the ATC but is that the right thing to do or should I just descent when I feel like doing it?
Their are precise ways to figure when to descend, but a commonly used rule of thumb is; altitude x 3 + 10. Example: altitude is 25,000 ft x 3 is 75 miles plus 10 = descent at 85 miles from destination. So at 85 miles, if you are IFR, you start asking ATC for lower.
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Agree with the other two posters.
Also, to make the 3 to 1 work:
Rate of descent is either 5x your ground speed or half your ground speed x10.
So:
300kts x 5 = 1500FPM
300kts/2 = 150 x 10 = 1500FPM
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Thank you all 3 these all were help full but I have a question for @DismayingBroom1 I ask the ATC for any altitude that I want right?
ive always been taught the rule of 3 and 6
3x alt =distance
6x ground speed for decent speed
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It’s somewhere between 5 and 6 x ground speed for the rate of descent. I used to use 5 x then add a bit.
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DaFlame, yes, in increments of 1000 as offered. If I am at 25,000ft or higher I usually ask for a 10,0000 ft, descent depending on the terrain I am flying into. ATC usually steps you down once or twice anyway. If I am at 25,000 and select a 10,000 ft altitude change I will be asking for 15,000 ft flight level (actually I have my co-pilot handle all ATC comms). Typically but not always ATC will give me FL180 first with 3000 ft later.
Hope that is clear.
Happy Landing.
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Interesting, I’ve never heard that one.
I personally like the “divide by two x10” method just because I find it easier to take half of, say, 14 than multiply it by 5. Or 6.
In any case, it’s just a SWAG and will vary. 
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To me the other answers somewhat miss the point of your question.
If ATC tells you to descend “at pilot’s discretion” then yes, descend when and how you please. However, if you’re on an IFR flight plan and ATC tells you to descend you have to comply (for all intents and purposes). You do so as you feel is safe for your airplane, but you begin your descent when instructed to do so.
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You don’t blindly rely on ATC its good to have an idea when you’re reaching TOD but if youre on a vfr flight then you DO need to know. also ATC in MSFS so ■■■■■■ half of the time you dont get any descent info at all
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So I have a question yesterday I was doing a flight on the a320 and I was at FL360 (36,000 ft) and I did the math u told me to do 36,000 x 3 = 10800 miles + 10 = 10810 so 10810 nm is when I should start desent right? And if I’m right where will it show me how far I am from my dest on the default a320?
Hm, the math is way off there. 10,810 nautical miles is just a little halfway around the world.
Here’s a better way to think about this:
NOT TAKING INTO ACCOUNT GROUND SPEED, let’s just do a quick Top of Descent (ToD) math. It’s really simple.
Let’s assume you need to be at 4,000 feet at the initial approach into your destination airport - this number would vary depending on which actual airport and approach, but it’s a good round realistic number.
(Your Current Altitude MINUS Target Altitude)*3) / 1000 = TOD Distance from airport.
((36,000 - 4,000) x3) / 1,000 = 96 Nautical Miles.
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You actually knock the last 3 zeros off the altitude, so generally from 32000 feet it would be 32x3=96 miles (approximately) where you would want to start the descent.
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That’s right
…when my third party apps and flight computer(depending on the aircraft) tell me to. Jk. Sometimes you gotta break out a calculator and do some old school math.
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I tried that on a calculator but it gave me 0.096
I also tried that on a calculator but it gave me 35988.. so is that right?
If you’re at 32000 feet, drop the last 3 zeros. Then you have 32, and multiply that by 3, which gives you 96. It’s rough but very close.
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36,000 - 4,000=32,000
32,000 x 3=96,000
96,000 ÷ 1000=96
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