For the sake of truth in advertising, I am going through very similar calculations right now. We had a certain sum set aside in a cash account to cover an addition / remodeling project. We hired the architect and got construction bids, and the total came in higher than we had guessed. Rather than scale back the plans we took the leap of faith for the whole hog. To make up the difference we took cash out of our refinance, which had been planned to take advantage of a rate drop anyway. Our total mortgage even with the cash out is about 50% of the house value (before the addition) so I don't feel like we are over-exposed there. With the rate drop our monthly payment is unchanged. I think we are close enough to be able to handle the remaining gap with a little belt-tightening. To be honest, though, we did evaluate whether we'd be willing to slow down our retirement contributions if necessary to make up the difference. We are totally maxing out all tax advantaged contributions in 403B, two Roths, and a SEP IRA, so we could easily get what we need with a 20% reduction in new contributions over the next year. That's the functional equivalent of withdrawing, so I'm sympathetic to what you are contemplating.