Best strategy for 4daily!

This is my suggestion. First, you will get you money back in 45 days.
Then, you can continue to surf and collect your profits.

1. You start on 1st of month, say 1st May 2005 with your $1000 upgrade.

2. Surf daily and when you reach more than half, upgrade using your earning. At day 13, your earning will be 13x4%=52%.
So you will earn 520 and you upgrade all of this. Your level now becomes $1520.

3. Now surf daily until end of month and no upgrade.
Your earning will be 18x4%x$1520=$1094.40 on May 31.

4. On 1st Jun, you upgrade $688 from your earning so that your level becomes $2188. This brings your minimum cash out to $1094 (slightly lower than your May 31 earning), and your balance is $406.40.

5. Surf until 15 June without any upgrade. Your earning will be 15x4%x$2188=$1312.8. At this time, you are qualified for the cash payout. You meet both conditions.
a. Your end of last month earning $1094.40 is higher than the minimum cash out of $1094.
b. Your current cash balance $1312.80 is also greater than the minimum cash out of $1094.
Thus, you get your money back in 45 days. You get a cash payout of $1094.40 with a balance of $218.40

6. Surf for another 5 days at this rate and you earn 5x4%x$2188=$437.6 and on 50th day (20th June) your balance becomes $437.60+$218.40=$656.

7. On 51st day, your initial $1000 expires. Your level now reduces to $1188 and min cash out is $594. Since your cash balance $656 is higher than min. you can upgrade again with this earned money.
You upgrade all the amount, and your level returns to $1844.

8. You surf until end of June and earns 10x4%x$1844=$737.60 and you will cash out this amount on 15th July. You are not quite double your money, but close...

9. You can continue with the above itteration to meet your target.

good luck!