Leverage Decay: The Index Came Back, You Didn't
Enter daily percentage moves to see what a 2x leveraged product is actually left with. It tracks twice the daily return, not twice the period return.
A 2x leveraged product tracks twice the daily return, not twice the return over your holding period. Those sound similar. They are not.
The default sequence is -20, 25: down 20%, then up 25% — the index lands exactly back where it started. The 2x product falls 40%, rises 50%, and ends at 90.
What it charges you is not a fee. It is the volatility itself. The longer you hold and the choppier the ride, the wider the gap — which is why it is built as a short-horizon trading tool, not a position. That is not an opinion; it is the product’s design.
同一段行情來回三次：指數還是 100，兩倍槓桿只剩 72.9。震盪愈多次，缺口愈大。看這個概念是怎麼來的 →
Source
// 兩倍槓桿追蹤的是「每日報酬的兩倍」，不是「期間報酬的兩倍」。
// 所以要逐日相乘，不能把整段報酬乘二。
let index = 100;
let lev = 100;
parts.forEach((pct) => {
const r = pct / 100;
index *= 1 + r;
lev *= 1 + k * r; // k = 槓桿倍數
});
// -20, 25 走三次：index 回到 100，lev 只剩 72.9。
// 少掉的 27.1 不是手續費，是波動本身。
const shortfall = index - lev;