The BIFF method: how to reply to a hostile co-parent or ex

If you co-parent with a high-conflict ex, you already know the pattern. A message lands that is sarcastic, accusing, or designed to push exactly the button that gets a rise out of you.

You draft three paragraphs defending yourself, delete them, write them again, and lose an evening to it. The BIFF method exists to break that cycle. It is especially useful when co-parenting with a narcissist or anyone else who argues over every word.

BIFF was developed by Bill Eddy at the High Conflict Institute as a practical formula for responding to hostile email and messages. It is widely used by family lawyers, mediators and co-parenting coaches because it does one thing very well: it lets you answer what genuinely needs answering while refusing to be pulled into the fight. This guide explains what BIFF is, how to write one, and how to keep your replies calm even when the incoming message is anything but.

What the BIFF method is

BIFF is an acronym for the four qualities a good reply to a hostile message should have:

• Brief. A few sentences, not paragraphs. The longer your reply, the more material you hand the other person to argue with.
• Informative. Stick to the useful facts: a time, a date, an answer to a direct question. Leave out opinions, defences and history.
• Friendly. A neutral, civil tone. Not warm, not cold, not sarcastic. Just polite enough that no one could read it as an attack. If you want a slightly warmer tone, the yellow rock method builds on the same idea.
• Firm. Close the topic. A BIFF reply does not invite more back-and-forth, ask loaded questions, or leave the door open to an argument.

The point of BIFF is not to win the exchange or get the other person to admit anything. It is to end your part of it cleanly, protect your own peace, and leave a record you would be comfortable having anyone read.

When to use a BIFF response, and when not to

BIFF is for messages that are hostile but still need a response. The classic case is a co-parenting message wrapped around a real question: “You are unbelievably selfish for changing the weekend, my lawyer will hear about this, and what time are you dropping the kids on Friday anyway?” Buried in the provocation is a logistics question that genuinely needs an answer. BIFF lets you answer the question and ignore the rest. Our guide on how to respond to a narcissist shows the same approach across more situations.

It is just as important to know when not to reply at all. If a message is pure provocation with no decision attached (no question, no logistics, nothing that requires you to act), then the strongest response is often silence. Not every message deserves an answer, and replying to bait simply because it arrived only invites more of it. When you do reply, the grey rock method of flat, uninteresting answers pairs well with BIFF.

How to write a BIFF reply, step by step

The method is simple to describe and harder to do when you are upset. These steps make it easier.

1. Pull out the one thing that needs an answer

Read the message once, then find the single fact or decision it actually requires. Ignore the adjectives, the accusations and the digs. Everything else is noise you do not have to engage with.

2. Write only that, in two or three sentences

Answer the question plainly. “Friday pickup is 5pm at the usual place. That still works for me.” You do not need to acknowledge the insult, justify your earlier decision, or correct their version of events. Holding that line is one of the core co-parenting boundaries.

3. Strip out every reaction

Read your draft back and delete anything that is defending, explaining, blaming or scoring a point. If a sentence would not exist in a message to a neutral colleague, cut it. This is the step that turns a normal reply into a BIFF reply.

4. Close it, do not open it

End on something final rather than a question. “Let me know if Friday changes” is fine. “Why do you always do this to the kids?” hands them the next round. A BIFF reply should give the other person nothing to volley back.

5. Wait before you send

Give yourself a gap between writing and sending, even an hour. Re-read it cold. Hostile messages are designed to make you react fast, and the pause is where most of the damage gets caught before it goes out.

BIFF examples: before and after

Here is the difference in practice. The “before” is the reply most of us want to send. The “after” is the BIFF version.

Example 1: a schedule change

Their message: “Typical of you to change the handover at the last minute. The kids are confused and it’s entirely your fault. What time is it even happening now?”

Before (reactive): “It is NOT last minute, I told you on Tuesday, and the only person confusing the kids is you. Maybe if you actually read my messages...”

After (BIFF): “Handover on Saturday is now 10am at the usual spot. I’ll have their bags packed and ready. Thanks.”

Example 2: an accusation about money

Their message: “You still haven’t paid your share of the school fees. You clearly care more about yourself than your own children.”

Before (reactive): “How dare you. I have paid for everything for years while you contributed nothing, and you have the nerve to lecture me about the children?”

After (BIFF): “I transferred the school fees on the 3rd. I’ve forwarded the receipt so you have it on file. Let me know if it hasn’t arrived.”

BIFF and assertive communication

BIFF is a practical form of assertive communication: saying what you need clearly and respectfully, without attacking the other person and without giving in. It sits between two common traps. A passive reply apologises, over-explains and agrees to things you don’t want. An aggressive reply hits back. An assertive reply states the facts and your position, then stops.

• Passive: “Sorry, I know it’s my fault, I’ll sort it all out and pay for everything.”
• Aggressive: “Typical. You never plan anything, so don’t blame me.”
• Assertive (BIFF): “The invoice is attached. I’ll pay half by Friday, as we agreed.”

If you tend towards the passive side, our guides on fawning in messages and how to stop people pleasing cover why it happens and how to change it. For setting limits on how and when someone contacts you, see how to set boundaries by text.

Common mistakes that turn a BIFF reply hostile

Most BIFF replies fail in predictable ways. Watch for these:

• The sneaky dig. One sarcastic word (“Obviously the pickup is at 5pm, as I already told you”) undoes the whole thing. Drop the “obviously” and the “as I already told you”.
• Over-explaining. If you find yourself justifying a decision, you have left BIFF. State the outcome, not the reasoning.
• The parting question. Ending with “Is that a problem for you?” reopens the fight you were trying to close.
• Matching their length. A long hostile message does not require a long reply. Brief is brief regardless of what landed in your inbox.
• Replying while triggered. The single biggest cause of a hostile reply is sending it in the first ten minutes. The pause is not optional.

Using FenceChat to keep BIFF easy

The hardest part of BIFF is not the formula. It is staying calm enough to use it. When a hostile message hits your normal inbox or phone, you read every word of the abuse before you get to the one question that matters, and by then you are already in fight mode.

FenceChat sits between you and a difficult ex. Their messages come in by ordinary email or text (they install nothing and set up nothing), and FenceChat screens out the hostility before it reaches you. You see the part that needs a decision without absorbing the attack around it. That makes a calm BIFF reply the natural response rather than a feat of self-control.

Every message in and out is also kept in your Archive, clean and dated, and you can export it at any time. So the BIFF replies you write are not just good for your peace today. They build an organised, factual record of your communication that you can hand to a lawyer or mediator if you ever need to.