Extract brewing - water amount

I am on my second batch and have a extract brewing question. I have a 5 gal kit, I want to end up with close 5 gal. On my last batch I ended up closer to 4 gal andI started with 5.5 gallon on a full boil. Can I just up beginning water amount to 6.5 gal without having to alter ingredients? Thx!

yes, if that is your boil-off rate. Another option is to top off your fermenter after everything else has been added so that you get your batch up to the size that you had planned. You can use pre-boiled tap water or bottled water to top it off. This has an advantage if you are using an ice bath to cool your wort because you can put a jug of bottled water in the fridge overnight and when you add it you will help cool down your wort.

So it doesn't water down the beer then?

Well, it depends what your recipe is. If your recipe is for a 5.0 gallon batch and you have 4.5 gallons post-boil, then topping it up with .5 gallons would water it down compared to 4.5g, but would bring it up to what the recipe calls for. Otherwise, your wort would have too high of a concentration of sugars, which would result in a higher ABV when the product is finish - potentially throwing off some of the balance in the recipe. You ultimately want the batch size at the time you pitch your yeast to equal the batch size of the recipe as intended. Going back to your first question, if you know how much water you typically boil off over the course of your brew session, there is nothing wrong with your approach of starting out with more water so that you end up with exactly the quantity of wort that was planned.

To get into a good habit for the future. You should be taking a OG reading before pitching your yeast. More advanced is using a refractometer so you can check the gravity while boiling. If your wort is supposed to be 1.050 for 5gal. And its 1.050 with 3-4gal then adding top off water will dilute it.

Extract has a measured amount of fermentible sugar in it from the plant. Packaging, sitting in a warehouse, sitting on your LHBS shelf only to reach you months later will have a impact. For these reasons i stay away from extract that comes in a transparent container. Or mass produced commercial stuff in a can.

I was having inconsistansy and stuck fermintations untill i really started checking my gravitys. I counter the dilution problem by having a few pounds on ultra light DME on hand to bring the OG where it needs to be.