Actually, most realtors will tell you that you can obtain financing with 10%, or even 3.5% financing (FHA), and technically they will be correct.
But let's do the math. Say, you are shopping for something that is going to sell for $550K. You have several choices:
1. Put 3.5% down, get FHA. Well, that means borrowing $531 K and paying 1 - 1.25 % ABOVE the best rate. Your expected monthly principal plus interest, roughly $2,450, at about 4.5 - 4.625%.
2. Put 20% down, get conventional. Well, that means borrowing $440K and paying somewhere between 0.375% - 0.5% ABOVE the best rate. Your expected monthly principal plus interest payment, roughly $2,100, at about 4.00 - 4.125%.
3. Put 25%, get true conventional, reduce your borrowed amount below $417K. Note that Fanny best rate for Condos is 25%, for under $417K. In this case, your payment (principal plus interest) will be $1,890.
So in case 3, you will pay roughly $1,890 vs case 1, in which you will pay $2,450, or a $560 a month difference. It is true, that in case 3, you will need $137K down vs case 3, only $20K.
Do note that unless specifically FHA, MOST banks will not even offer 2!!
But if you ask me, than (1) saving $560 a Month, or $6,700 a year is worth it for $115K in additional downpayment, (2) in a high cost area such as Northern Jersey commuter areas of Manhattan you need more money to play real estate.
I would HIGHLY recommend, that despite what the realtors and mortgagage broker say, not going for 3.5% FHA. It is a mistake that can cost you dearly down the road.