Fund calculator

fund_calc.py

# Requirements: pandas matplotlib

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
from matplotlib import ticker

# Parameters
monthly_investment = 50
simulation_monthly_rates = [0.00, 0.0137, 0.0359]  # All the monthly rates to simulate
total_simulation_years = 20  # Total number of years to simulate future value

# List of (loss_probability, [loss_percentage1, loss_perc2, ...])
monthly_loss_map = [
    (0.1, [0.1, 0.6]),
    (0.01, [0.1, 0.6]),
]
monthly_loss_map = sorted(monthly_loss_map, key=lambda v: v[0])

# Set a seed for reproducibility
np.random.seed(42)  # TODO Run simulations on multiple seed and pick best and worst

# Simulate the future values
results = {}

# Simulate each monthly rate
for r in simulation_monthly_rates:

    fv = []
    # We start the first month with a base investment
    monthly_fv = monthly_investment
    for y in range(total_simulation_years):
        for m in range(12):
            # Simulate probability of loss

            prob = np.random.rand()
            for entry in monthly_loss_map:
                if prob < entry[0]:
                    # Monthly loss
                    monthly_fv -= monthly_fv * np.random.choice(entry[1])
                    break

            # Monthly win + new investement
            monthly_fv += monthly_fv * r + monthly_investment

            fv.append(monthly_fv)
    results[f"Monthly return, price rate: {int(r * 100)}%"] = fv

tot = []
total_invested = 0
for y in range(total_simulation_years):
    for m in range(12):
        total_invested += monthly_investment
        tot.append(total_invested)

results["Total Invested"] = tot

pd.options.display.float_format = "{:,.2f}".format
df = pd.DataFrame(results)
df.index.name = "Months"
print(df.round(2))

ax = df.plot()
ax.set_xlabel("Months")
ax.set_ylabel("Monthly Future Value (€)")
ax.set_title(
    f"""€{monthly_investment}/Month, Total Invested : {results["Total Invested"][-1]} in {total_simulation_years} years."""
)
ax.grid(True)
ax.yaxis.set_major_formatter(
    ticker.StrMethodFormatter("{x:,.0f}")
)  # Adds commas and no decimals
plt.tight_layout()
plt.show()