You can lose weight surprisingly fast in the short term, but safe, realistic fat loss for most people is about 0.5–1 kg (1–2 lb) per week, and anything much faster than that is usually hard to sustain and can have health risks.

Quick Scoop: The Numbers

  • A commonly recommended, safe rate is 0.5–1 kg (1–2 lb) per week for most adults.
  • Doctors usually call anything faster than about 1 kg (2 lb) per week “rapid weight loss.”
  • Under strict medical supervision with very low‑calorie diets (around 800 calories/day), some people can lose about 1.5–2.5 kg (3–5 lb) per week for a short period (up to ~12 weeks), but this is not meant for unsupervised DIY dieting.
  • Crash diets and extreme methods may show big scale drops at first, but much of that is water, glycogen, and sometimes muscle rather than pure fat.

Typical timelines

  • Lose 5 kg (11 lb) safely: ~5–10 weeks at 0.5–1 kg/week.
  • Lose 10 kg (22 lb) safely: ~10–20 weeks.
  • Lose 20 lb “fast but still sane”: experts suggest planning for 10–20 weeks, not 2–4.

What “Fast” Really Means

Fast weight loss sounds exciting, but your body reads “extreme deficit” as stress. Usually safer / more sustainable:

  • Moderate calorie deficit (e.g., 400–700 calories below maintenance, depending on size).
  • 150–300 minutes/week of moderate to vigorous cardio (20–40 minutes most days).
  • Strength training 2–3 times per week to protect muscle and metabolism.
  • Some people add intermittent fasting (like 16:8 or 5:2) as a structure that makes a moderate deficit easier to stick with.

Usually risky when done alone without medical help:

  • Very low‑calorie diets (around 800 calories/day) beyond a short period or without supervision.
  • “Detoxes,” extreme cleanses, unregulated fat‑burner supplements, or laxatives and enemas used for “weight loss.”

Rapid approaches are sometimes used before surgery or in clinically supervised obesity programs, not as casual at‑home hacks.

What You Actually Lose at First

When the scale suddenly drops, it’s not all fat.

  • First 3–7 days: lots of water and glycogen loss, especially if you cut carbs or sodium; this can be several pounds.
  • Ongoing weeks: a mix of fat, water, and some muscle; resistance training and adequate protein skew this more toward fat loss.
  • Day‑to‑day: scale can jump up or down 0.5–2 kg (1–4 lb) from water, digestion, and hormones, even if fat is slowly trending down.

This is why someone can “lose 5 lb in a week,” but only a fraction is true fat loss.

Fast vs. Sustainable: Two Lenses

You can think about “how fast can you lose weight” in two ways.

1. Theoretical maximum (not recommended without doctors)

  • Very low‑calorie diets (VLCDs) with medical monitoring can create very large deficits, leading to perhaps 1.5–2.5 kg (3–5 lb) per week for a limited time.
  • These are usually done with specially designed meal replacements, blood tests, and regular check‑ins because of risks like gallstones, nutrient deficiencies, and metabolic slowdown.

2. Real‑world “I want to keep this off”

  • For most people, 0.5–1 kg (1–2 lb) per week is the sweet spot: noticeable, but not so aggressive that you burn out.
  • Many long‑term success stories actually average a bit slower than this, especially once they get closer to goal weight.

A lot of people in online weight‑loss communities describe their success as “slow and boring but consistent” rather than dramatic.

If You’re Thinking About Going “Very Fast”

If you’re considering anything that might push you over about 1 kg (2 lb) per week:

  1. Talk with a doctor or qualified professional first, especially if you have any health conditions, take medications, or have a history of disordered eating.
  1. Prioritize muscle and health:
    • Keep protein reasonably high.
    • Include strength training.
    • Watch for fatigue, dizziness, hair loss, or mood changes as red flags.
  2. Ask “Can I see myself doing this for months?” If not, it’s probably too extreme to be your main strategy.

Information gathered from public forums or data available on the internet and portrayed here.