Safe withdrawal rates, honestly

What the rule says

Withdraw 4% of a diversified stock/bond portfolio in your first year of retirement, then adjust that dollar amount for inflation every year after. In historical US data (the research behind this is the 1998 “Trinity study” and William Bengen's earlier work), a portfolio managed this way survived essentially every 30-year retirement since the 1920s — through the Depression, stagflation, and several crashes.

Inverted, it gives the planning shortcut everything else rests on: to spend $X per year, you need 25×X invested (100 ÷ 4). Spend $4,000/month → $1.2M. WorthCurve uses exactly this, with the rate adjustable, and computes the target on net spending — what the portfolio must cover after bridge income, Social Security, and pensions.

What it quietly assumes

• A 30-year horizon — retire at 40 and you're asking for 50+ years, where the historical success rate is lower.
• US historical returns — arguably the best market run in modern history.
• Mechanical behavior — never cutting spending in bad years, never panicking out of stocks.
• No fees or taxes — a 1% advisory fee effectively turns 4% into 3%.

How to actually use it

• Long horizon? Consider 3.5%. If your change comes decades before a traditional retirement age, 3.5% (a ~29× target) buys meaningful headroom for a modest cost.
• Flexibility is worth more than precision. The ability to trim spending 10% in a bad market, or earn a little, does more for plan survival than the difference between 3.8% and 4.1%.
• Treat it as a heuristic, not a contract.It answers “roughly how big must the portfolio be?” — the drawdown itself is better simulated month by month, which is what your plan does, alongside a conservative case.