Implied repo is your return for shorting the future and buying the deliverable bond. At the same time, the CTD is determined by the lowest net basis, which is your cost adjusted for carry. The bond with the highest implied repo and the lowest net basis is your CTD. For example, TUZ8 is the December two year futures contract. Once you bring that up, add the custom bonds and then just play around with the yields shifting the spreads between the current CTD and the hypothetical bonds. They show the implied repos too on the screen. Treasury Bond Futures 1 Treasury Bond Futures Basic Futures Contract Futures vs. Forward Delivery Options –Underlying asset, marking-to-market, convergence to cash, conversion factor, cheapest-to-deliver, wildcard option, timing option, end-of-month option, implied repo rate, net basis Concepts and Buzzwords Reading