I've heard block.timestamp can be manipulated by miners, and as I am writing a contract that uses block.timestamp in crucial functions, I am wondering how best to mirror its behavior using block.number

1 Answer 1


The timestamp can be manipulated to a small degree (unless a majority of miners are colluding, in which case all bets are off) since overtly abnormal timestamps will be rejected by other mining nodes.

block.number is presently a very unreliable method of measuring time (even for medium-term applications). Firstly, the time between blocks is already changing regularly due to the difficulty bomb. Then, there is the proposed delay of the difficulty bomb -- which means you have to figure out whether it will happen. Then there's a potential for a change in block time at some other point in the future -- and all bets are off when we have proof of stake. So not only would I not recommend using block.number for counting time for medium- and long-term periods, it is not really possible, unless you can predict the future.

For short-term intervals (and before integral steps in difficulty change from the difficulty bomb are accounted for), you can use the average time for a block to be mined and multiply to create a time measurement. Approximate time elapsed is average time multiplied by block time.

  • That makes sense - but I think timestamp could matter a lot in my application. I have a betting pool essentially that, if someone bet and then submitted a block immediately after, could shut out other bets and win a portion of the pool. What I'm trying to get at is that the timestamp may be manipulatable by a small degree, but it could be pretty important for my application.
    – A. Wade
    Commented Aug 14, 2017 at 18:33
  • 1
    If you're trying to do something like betting on some event at a particular time, the average block time calculation will be less accurate than the timestamp. Even changing difficulty will cause problems -- and variance will cause more issues by itself in a single block than timestamp drift from attack.
    – lungj
    Commented Aug 14, 2017 at 19:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.