Find the benefit of investing in a CD Ladder compared to the High Yield Online Savings account given some assumptions

cd_ladder.py

# coding: utf-8
'''
### Benefits of CD Ladder vs. Online Savings
Find the benefit of investing in a CD Ladder compared to the High Yield Online Savings account given some assumptions.

Assumptions:
* Investment in CD Ladder for various buckets; not the highest CD bucket rate available for the term.
* Only considers CD buckets that have the higher interest rate than the online savings account.
* Equal distribution into each selected bucket; based on the above assumptions.
* Automatic renewal of the CD at the end of the CD bucket term for the numbers of years specified.
    * If renewal is over the numbers of years specified, the renewal will be ignored and the money from that bucket will not be invested again.
'''

# #### Inputs:
amount_to_invest = float(10000.00)
number_of_years_to_invest = int(5)

# Goldman Sachs Online Savings interest rate
high_yield_savings_rate = {1: 0.012}

# cd rates from Barclays Online CDs
cd_rates = {0.25: 0.0035, 
            0.50: 0.0055, 
            0.75: 0.0060, 
            1: 0.0144, 
            1.5: 0.0149, 
            2: 0.0169, 
            3: 0.0193, 
            4: 0.0203, 
            5: 0.0227}

# #### Calculations:
def compound_interest(principal, rate, payments_in_year, number_of_years):
    return principal*(1+(rate/payments_in_year))**(payments_in_year*number_of_years)

# amount at the end of the term if invested into savings
# a = principal(1 + (rate/num of payments in year)^(number of payments in year * years to invest)
interest_in_savings = compound_interest(amount_to_invest, high_yield_savings_rate.get(1), 12, number_of_years_to_invest) - amount_to_invest
print("Interest earned while investing in a High-Yield Savings Account for {0} years: ${1:.2f}".format(number_of_years_to_invest, interest_in_savings))

# assuming equal distribution for initial investment where the % is more than the savings rates
# assuming automatic renewal of the CD with the interest earned at the end of each term
where_to_invest = {k: v for k, v in cd_rates.items() if v > high_yield_savings_rate.get(1)}
amount_to_invest_in_each_bucket = amount_to_invest / len(where_to_invest)
print("Investing ${0:.2f} in the following CD buckets: {1}".format(amount_to_invest, where_to_invest))

# for each key value pair in the cd_rates
# if the value of the key is greater than the savings rate
# then find the amount at the end of the years to invest term
total_interest_earned_from_cd = 0
for k, v in where_to_invest.items():
    amount_at_end_of_term = compound_interest(amount_to_invest_in_each_bucket, v, 1, int(number_of_years_to_invest/k)*k)
    total_interest_earned_from_cd += (amount_at_end_of_term - amount_to_invest_in_each_bucket)
    print("Investing in a {0:<4} year CD @ {1:.2%} {2} time(s) will result in ${3:.2f} at the end of the {4} year term".format(k, v, int(number_of_years_to_invest/k), amount_at_end_of_term, number_of_years_to_invest))

print("Interest earned while investing in a {0} year CD Ladder: ${1:.2f}".format(number_of_years_to_invest, total_interest_earned_from_cd))

print("You will have an additional ${0:.2f} if invested in a CD ladder for {1} years with the assumptions stated above.".format(total_interest_earned_from_cd - interest_in_savings, number_of_years_to_invest))