Zestimates are not something you should use at all during the process of homebuying. They're notorious for being inaccurate, and can fluctuate quickly and wildly. They also aren't necessarily looking at the same things appraisers are looking at. Whether or not your appraisal will come in low or at asking (or above which can still happen) depends a lot on the market and the individual neighborhood you're buying in. We just bought around Santa Barbara, and our realtor was confident the place we bought would appraise, but I was still a bit surprised when it did appraise, given how much we offered and what we were getting for the price. How low was the appraisal?