A brewed cup of decaf coffee carries about 2 to 7 mg of caffeine. A regular cup carries 80 to 100 mg. That is the entire headline. Decaf is roughly 97 to 99.9% caffeine-free, depending on the method, the batch and the brew, but it is never 100% caffeine-free. UK and EU law allows up to 0.1% residual caffeine on a dry-matter basis in the roasted bean, and that is the rule every commercial method has to clear before the word decaf can go on the pack.
This page is the map of the whole caffeine question. What is actually in the cup, why there is anything at all, what the label is and isn't required to tell you, and how to switch without the headache. Each numbered topic has its own full guide linked at the bottom.
What's actually in the cup
The 2 to 7 mg figure is the population average for a 240 ml brewed cup, drawn from method-supplier data and independent lab testing. The variance is real. Sugar cane EA decaf tends to test slightly higher, Swiss Water and CO2 tend to test slightly lower, but the gap between methods is smaller than the gap between batches of the same coffee. A 350 ml mug brings you to roughly 4 to 12 mg. A double espresso made with decaf beans is roughly 4 to 10 mg. None of these are biologically active doses of caffeine. For context, the alertness threshold sits somewhere around 40 to 50 mg, and even the most caffeine-sensitive people don't usually feel anything under about 20 mg.
If you're trying to calculate a daily total, count decaf at 5 mg per cup as a sensible working figure. If you're trying to calculate the headroom under a clinical or pregnancy limit, count it at 7 mg per cup to be safe.
Why there's any caffeine left at all
No commercial decaffeination method removes 100% of the caffeine. The chemistry is the reason. Caffeine is bound up inside the cellular structure of the green bean, and the last few percent of it sits in the toughest places to reach. Pushing the extraction harder to chase the final 0.5% strips out flavour compounds at a rate that makes the coffee taste flat. The trade is between caffeine removal and cup quality, and every method picks a stopping point. Swiss Water and most CO2 plants stop around 99.9%. Sugar cane EA plants stop around 97%. Methylene chloride plants stop around 99.9% for the indirect Euro process, and around 97% for the older direct process. The legal threshold catches them all.
How decaf compares to other drinks
Caffeine numbers across common UK drinks, for context.
| Drink | Caffeine per typical serving | Notes |
|---|---|---|
| Decaf coffee (brewed) | 2 to 7 mg per 240 ml cup | 4 to 12 mg in a mug. Negligible biologically |
| Decaf espresso | 4 to 10 mg per double shot | Higher concentration, lower total volume |
| Regular filter coffee | 80 to 100 mg per cup | 120 to 180 mg in a mug |
| Regular espresso | 60 to 80 mg per double shot | Less than people assume |
| Black tea | 40 to 70 mg per mug | Brew time is the lever |
| Decaf tea | 2 to 5 mg per mug | Same regulatory logic as decaf coffee |
| Cola (330 ml can) | 32 to 42 mg | Less than a tea, often more than a decaf |
What the UK label is required to tell you
Less than most people assume. UK retained EU food law caps methylene chloride residue at 2 mg/kg in the roasted bean (Regulation 1881/2006), and the threshold for being sold as decaf is 0.1% caffeine on a dry-matter basis. Beyond that, brands don't have to name the decaffeination method on the pack. Pre-packed coffee falls under the standard food information requirements, so the brand name, country of origin, weight and roast date are mandatory, but Swiss Water, CO2, sugar cane EA and methylene chloride are all just commercial choices in how the coffee was made, not regulatory disclosures.
The practical rule is straightforward. If the label says Swiss Water, CO2 or Sparkling Water Process, or sugar cane EA, the brand is choosing to disclose because the method sells. If the label says nothing at all, the method is almost always methylene chloride or synthetic ethyl acetate, because there's no commercial reason to disclose either. The honest version isn't chemical-free vs natural. It's disclosed vs undisclosed.
How to switch to decaf without the crash
The caffeine withdrawal headache is the single biggest reason people fail at switching. The half-life of caffeine sits around 5 hours, the withdrawal peak hits 24 to 48 hours after the last full dose, and a heavy regular drinker (4+ cups a day) can carry the headache for up to a week if they switch cold. The fix is to taper. Half-caf for a few days, then a 75/25 blend of decaf and regular, then 25/75, then full decaf. Two weeks of gradual swap is enough for most habits. The full sequence with the brand picks is in the switching to decaf playbook.