Write some Software

I am looking to have a simple program created for an investment program. It will need to have a simple interface and can be excel based but I want it to look finished and professional. The program itself will allow the user to enter and initial investment in US Dollars - It will calculate the daily interest paid but there is 4 levels There needs to be a place to enter a daily interest rate percentage Then there should be a spot that will let there be an extra percentage rate too that is a bonus depending on how large the investment is. Here are the levels: Lending amount Interest (Accrued daily) Capital release $100 - $1000 Volatility software interest After 299 days $1010 - $5000 Volatility software interest + 0.10 % daily After 239 days $5010 - $10,000 Volatility software interest + 0.20 % daily After 179 days $10,010 - $100,000 Volatility software interest + 0.25 % daily After 120 days There should be a spot where the user can pick the amount of reinvestment is $10 increments. These need to follow the same rules above so that the bonus interest can be added. As the interest paid reaches the minimum it should make the $10 reinvestment and the remainder should stay in the account till it reaches the minimum reinvestment again. If they chose $10 but as they make more than $20 a day it should reinvest whatever multiple of $10 available. Same thing if they pick reinvestment of $1010 it should build up to the amount to reinvest and save the remainder and so in until they have enough to reinvest $1020 and so on in $10 increments. Each loan and reinvestment has its own interest terms and interest bonus so it needs to be applied correctly to calculate the growth correctly One thing if the user puts $10010 in originally so they will be getting the .25 bonus that should calculate but then if the reinvestment is only $10 the calculator must recognize that and not add the bonus percentage. The system should show all the calculations so the user can see how their investment is growing each day - Maybe using different colors as the amount off reinvestment grows from $10 -$20-$30- $100 extra. I will attach an Excel spread sheet I was using but it doesn't correctly do the interest when large 1st loan but the investment are small.