How long does it take to learn a language?

No one has measured how long you will take, and a calculator that pretends otherwise is guessing. This one combines two published figures and shows its working, so you can judge it yourself.

1. Cambridge English estimates the cumulative guided learning hours to reach each CEFR level:
   • A2: 180–200 hours
   • B1: 350–400 hours
   • B2: 500–600 hours
   • C1: 700–800 hours
   Those hours were measured for learners of English, and are counted with a teacher — not including homework or practice outside class.
2. The US Foreign Service Institute groups languages by how long English speakers take to reach professional working proficiency in full-time class. We divide each category's hours by Category I's midpoint (675 hours):
   • Category I: 24–30 weeks, 600–750 class hours → multiplier ×1.0
   • Category II: 36 weeks, 900 class hours → multiplier ×1.33
   • Category III: 44 weeks, 1,100 class hours → multiplier ×1.63
   • Category IV: 88 weeks, 2,200 class hours → multiplier ×3.26
3. FSI measured English speakers. If you already speak a close relative of the language — Ukrainian or Russian for Polish, Spanish for Portuguese, Dutch for German — you have the head start English speakers have with Category I languages, so the estimate uses ×1.0 instead.
4. Every other language you speak helps too, and more so when the new one borrowed from it: Polish took many words from French, Japanese and Korean from Chinese, Tagalog from Spanish. We take 10% off for shared vocabulary and 3% for each language you already speak (up to 3), never more than 20% in all. Research agrees on the direction but gives no rate to copy, so these are our allowances, not measurements.
5. Age: studies agree that adults learn quickly at first and that the hours you put in matter more than your age, but none gives a reliable rate per age. We add a cautious allowance of our own — Under 18: +0%, 18–29: +0%, 30–44: +10%, 45–59: +20%, 60+: +30% — so treat that part as our assumption, not a measurement.
6. hours = Cambridge hours for the target level × multiplier × (1 − languages you speak) × age allowance, less the hours for the level you already have, divided by the hours you study each week.

Treat the answer as a planning range, not a promise. Self-study hours are not classroom hours, and hours spent only reading build a different skill from hours spent talking. What the arithmetic does show reliably is the trade-off: minutes a day, kept up, beat long sessions you skip.