IME, your time trial speed will drop about 0.6 mph on the day you donate blood. A few days later, you'll be off by 0.4-0.5 mph. The next week, you're looking at a 0.2-0.3 mph deficit. Two weeks later, maybe 0.1 mph, but you're getting into the noise. You don't lose fitness from donating blood, you just lose O2 carrying capacity. US blood banks have you wait 8 weeks to donate again, the implication being that this is how long it takes to fully recover. You can get into long term iron deficit, but iron supplements or a high-iron diet can deal with that. You have to monitor your Hct, and if it starts to drop, take some iron pills.howardpowered said:I'm planning on giving blood soon, and I want to know from those racers out there who have done it how long it takes to recover. How will it affect my fitness, if at all, and how long until I'll be back to the good form I've got now?