図：VT v.s. オルカン (in NISA)

https://gyazo.com/fa6cec179830fb626897f04274bea3ff

図：5%成長するファンドが2%配当金を払う場合と払わない場合の基準価額#64d4b8bf774b1700005d79ddをかえただけ

code:main.py

import matplotlib.pyplot as plt

# 定義された条件

annual_growth_rate_ac = 0.05-0.0015

annual_growth_rate_vt = 0.05-0.0007

dividend_rate = 0.02

initial_investment = 10**7

investment_period = 20

us_tax_rate = 0.1

jp_tax_rate = 0.2

# 資産推移を保持するリスト

nisa_account_final = initial_investment

non_nisa_account_final = 0

regular_growth = initial_investment

# シミュレーション

for year in range(1, investment_period + 1):

dividend_nisa = nisa_account_final-1 * dividend_rate * (1 - us_tax_rate)

nisa_growth = nisa_account_final-1 * (1 + annual_growth_rate_vt - dividend_rate)

nisa_account_final.append(nisa_growth)

dividend_non_nisa = non_nisa_account_final-1 * dividend_rate

# 米国税を差し引く

dividend_non_nisa_after_tax = dividend_non_nisa * (1 - us_tax_rate) * (1 - jp_tax_rate)

# 税額控除のために米国勢を計算しておく

us_tax = dividend_non_nisa * us_tax_rate

# 米国税を差し引いた後の配当を加算

non_nisa_growth = non_nisa_account_final-1 * (1 + annual_growth_rate_vt - dividend_rate) + dividend_non_nisa_after_tax + dividend_nisa + us_tax

non_nisa_account_final.append(non_nisa_growth)

regular_growth.append(regular_growth-1 * (1 + annual_growth_rate_ac))

# 相対誤差の計算

relative_error = (n + nn - rg) / rg * 100 for n, nn, rg in zip(nisa_account_final, non_nisa_account_final, regular_growth)

# グラフの描画

fig, (ax1, ax2) = plt.subplots(2, 1, figsize=(10, 10))

ax1.plot(nisa_account_final, label="NISA Account (Final)")

ax1.plot(n + nn for n, nn in zip(nisa_account_final, non_nisa_account_final), label="NISA + Non-NISA Account (Final)")

ax1.plot(regular_growth, label="Regular Growth (5%)")

ax1.set_ylabel("Amount (JPY)")

ax1.set_title("Investment Simulation Over 20 Years (Final Corrected)")

ax1.legend()

ax1.grid(True)

ax2.plot(relative_error, label="Relative Error (NISA + Non-NISA vs Regular Growth)", color="red")

ax2.set_xlabel("Year")

ax2.set_ylabel("Relative Error (%)")

ax2.set_title("Relative Error Between NISA + Non-NISA and Regular Growth")

ax2.legend()

ax2.grid(True)

plt.tight_layout()

plt.show()