My preferred retirement calculator is

http://www.flexibleretirementplanner.com/java/LaunchFRPWeb.h...

Here are inputs I use (and how I interpret them):

Current age, retirement age and life expectancy. Mostly self explanatory. Always make sure you have a 30 year retirement for best planning (better to die with money than to die destitute).
In my example I am entering 35 for current age and 53 for retirement age.

Inflation- 3.5% I use default then will adjust upward some once I see core numbers with 3.5%. Use default for example.

Investment tax rate- 15% is current long term capital gains rate. This has impact to point where you have taxable accounts. If you have state taxes, you need to add that to the 15% (for example if state rate is 4.5% and fed is 15%, total is 19.5%. Use 20% for example.

Income tax rate is federal+state income tax rate. If you are married making more than 70k taxable income this is 25% federal+ whatever your state bracket is. Use 30% for best planning (this is worst case- I think- for most people). Use 30% for example.

Taxable portfolio- enter present value of taxable accounts. I would NOT include EF in this.
In my example I am using $1000.

Tax deferred portfolio- enter current value of 401ks, rollovers and money you have NOT paid tax on yet. Use 92000 for the example.

Tax free portfolios. Enter current value of roth accounts here. Use 27000 for example.

Min 401k/IRA withdraw age- enter age you will begin withdraws from 401k/IRA. Use 53 for the example.

Taxable annual savings- Enter amount you put into taxable accounts on a yearly basis. Enter 6000 for example ($500/mo).

Tax deferred annual savings. Enter amount you contribute to 401ks, traditional IRAs or similar. Use 24000 for the example.

Tax free annual savings. Enter amounts you contribute to ROTH accounts. In example use 10500 ($5000 for me, $5000 for wife in IRA, plus wife contributes 1% of gross to a Roth 401k).

Investing style- choose aggressive. Note it gives %stocks-%bonds-%international (70-7-23). Also note it gives avg return and standard deviation (10.5% and 15.8).
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write down the following
moderate risk is 41-45-14
with returns of 8.5% and std deviation of 9.9%.

below avg risk is 30-60-10 with returns of 7.5% and std deviation of 7.1%.
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Annual retirement income- enter income from a job you will WORK at once retired. Leave at 0 for example.

Retirement income starts at age what? List age for new job. does not matter if income is blank for the example.

Annual retirement spending. Enter your annual expenses you will need in retirement. Enter 60k for the example.

In upper right corner there is an "additional inputs", click that button.

set 3 different portfolio return criteria:

1) start of plan to end at age 45; rate ot 10.5%, std deviation of 15.8 (this is the aggressive choice). Click add.

**this is because I plan to be aggressive in investing style until age 45. 8 years from retirement the plan is to tone this down some.**

2) age 46 to retirement year, use a rate of 8.5 and a std deviation of 9.9. Click add.
**this is a move to a 60-40 type portfolio while working but before retirement**

3) retirement year to end of plan, use a rate of 7.5% with a std deviation of 7.1%. Click add.
**This is a 40-60 portfolio which is quite moderate (and should yield more than 4%).**

At bottom of this same window, add SS.

cashflow type: SS
start year age 62
end year (end of plan)
annual amount: $12000 (this is less than one half my projected benefit- I plan to take SS early at age 62).
Taxable percent: 85 (this is because if gross income+ 1/2 of SS is over 44k, SS gets taxed).

click add

add in SS for spouse. I want my wife to get her full benefit. She'll probably live longer, so this is "worst case".

start:Age 71
end: end of plan
annual amount: 24000 (full benefit in todays dollars)
taxable percent: 85

click add
click done

at top of screen there is a "run simulation" button.

Click run simulation.
You see a probability of success of 84.7%. That works for me. I make note a few numbers:
Starting withdraw rate is 4.2% (goal is for 4%).
Portfolio value at retirement $1.4 M (goal is $1.5 M).

Now tweak some settings- note how the Roth account is depleted (green bars).

There is a spending config button in lower right of inputs.
Click config.

At bottom of form click the following
"take withdraws from taxable, then tax deferred, then tax free"
**this means tap the Roth accounts last (let them grow for as long as possible)**

click run simulation again.

Note the roth account has a higher balance in 2069 (age 96 for me).

There are some finanical planning things this calculator does not take into account, care to discuss?