### Author Topic: Crazy, Sloppy Math Question  (Read 2520 times)

#### oldtoyota

• Magnum Stache
• Posts: 3142
##### Crazy, Sloppy Math Question
« on: October 02, 2013, 07:27:58 AM »
Let's say you saved \$40K per year and needed \$400K to retire. If you wanted to do a sloppy calculation, couldn't you just say you'd have the necessary \$400K in 10 years?

This would not factor in compound interest, so you'd actually end up with more if the market did not completely tank. Is that right?

I realize this doesn't factor in how much you'd need to withdraw, but this calculation makes the assumption that \$400K is what is needed so future expenses would have been calculated already.

The above might seem like a nutty question, but I think it will help me understand how to calculate something else.

#### matchewed

• Magnum Stache
• Posts: 4322
• Location: CT
##### Re: Crazy, Sloppy Math Question
« Reply #1 on: October 02, 2013, 07:36:47 AM »
It would be extraordinarily simplified but yeah you could say that.

#### Kira

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• Age: 35
• Location: Columbus, OH
##### Re: Crazy, Sloppy Math Question
« Reply #2 on: October 02, 2013, 07:52:11 AM »
The only thing I'd think would mess up that calculation is inflation - 40k in year 1 is different than the 40k you save in year 10. But otherwise yes I don't see how you could come to another conclusion, mathematically.

#### eyePod

• Pencil Stache
• Posts: 966
##### Re: Crazy, Sloppy Math Question
« Reply #3 on: October 02, 2013, 08:08:01 AM »
Sure, but you'd be losing out on a ton of money.  Assuming 3% inflation and 7% return (for a 4% overall rate), you'd be 90k over the mark by year 9.

Also, if you include the interest above, you'd hit 400k in between year 8 and 9.

#### KittyFooFoo

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• Age: 32
• Location: NYC
##### Re: Crazy, Sloppy Math Question
« Reply #4 on: October 02, 2013, 09:45:02 AM »
A rough way to estimate how much \$X/year turns into after 10 years of investing:

Add half to \$X, maybe rounding down a little.  Multiply by 10.  (this is closeish to dividing X by 12 and multiplying by 173, which is the multiplier for monthly savings after 10 years, taking interest into account)

So in your case, you could ballpark the \$40k/year at \$600k after 10 years.

#### oldtoyota

• Magnum Stache
• Posts: 3142
##### Re: Crazy, Sloppy Math Question
« Reply #5 on: October 02, 2013, 02:00:10 PM »
Thank you! I am poking around and looking at numbers from different angles. This has been educational. =-)

#### oldtoyota

• Magnum Stache
• Posts: 3142
##### Re: Crazy, Sloppy Math Question
« Reply #6 on: October 02, 2013, 02:01:18 PM »
Sure, but you'd be losing out on a ton of money.  Assuming 3% inflation and 7% return (for a 4% overall rate), you'd be 90k over the mark by year 9.

Also, if you include the interest above, you'd hit 400k in between year 8 and 9.

Very good point! Being over would be okay though.