I'm under on my calories daily

Well, I don't know if I can consider myself a "seasoned veteran" but I'd say these are your options:

1. Start eating more healthy calories now
2. Go with what you're doing now and readjust when you hit that inevitable plateau.

I took avenue number dos thinking because I was so obese my body could handle a very large calorie deficit. I was right for a while, the problem was I didn't know when to start eating more to keep away that notorious "starvation mode" (and no, it's not a myth, it's one of your body's survival mechanisms). It has been quite a struggle to get past these plateaus & find the right calorie intake for my body. I just broke plateau #3 (yep, 3 plateaus since January). Just FYI, I'm now up to eating 90-100% of my exercise calories.
Before that first plateau, I was eating 0-10%. I learned my lesson the hard way. But at least I learned it. Seems like a lot of people just quit trying once they hit a major plateau like that. :ohwell:

My advice is to educate yourself more on the subject (which I know is what you're trying to do here) and do what you feel you need to do for yourselves. Everyone's different. It could be that the 2 of you can handle larger deficits for long periods of time. My body did it for 4.5 months. But it can't even handle a 1000 calorie deficit anymore. I'm happy to oblige by eating more.

I was always under my calorie goal as well...I talked to my doctor and she said as long as I am full and not starving myself then I am good...I am a smaller person so she recommended me not to go under 1000 calories a day typically I ate about 800-1000 I lost 34 lbs in 3 months once I reached my goal I added about 100 calories a week for a week until I got up to about 1400 calories a day I have maintained my weight now for 3 months! So in my opinion KEEP IT UP!!

I'd say if you are working out as much as you are ("work out 5 days a week and burn 500 to 900 calories a day"), you probably should be eating more calories than just the minimum. Your body needs the fuel to continue working hard and working as efficiently as it possibly can. In my opinion, I would eat more throughout the day. Eating throughout the day will help you sky-rocket your metabolism as well as get in all the calories you need to keep your body happy. This is what my typical eating schedule looks like (this is mine today).

5am-workout 1 hour
6:45am- breakfast (Scrambled egg whites on sour dough english muffin)
8:30am- morning snack (Wheat chex mix)
10:30am- morning snack (raw strawberry slices)
12:00pm- snack (light cheese stick)
1:00pm- Lunch (Whole wheat pasta with red sauce + steamed broccoli)
3:00pm- Snack (Raw natural almonds)
4:30pm- Snack (Apple w/ natural peanut butter)
6:00pm- Dinner (Salmon + small red baked potato+ asparagus)
7:00pm- possible snack (depends on what I'm feeling...I have 200 calories left)
10:30pm---BEDTIME!

I am initially granted 1450 calories a day. I typically burn about 550 calories a day, so I eat about 1900-2000 calories a day total. Now, I know this sounds like a lot. But, I am eating every 2 hours as you can see from my schedule. And if I don't eat at least every 2 hours...my stomach is killing me! Since I've started doing this I broke through a 4 month plateau. I attribute that breakthrough to eating more. I've also noticed my body has been able to do more, as far as workouts go. Before (even when I considered myself "in shape") I would get dizzy or lightheaded after a 30 minute workout. Now I can push through and do 60 minutes worth, no problem.

If you feel at first eating that many calories is too much...gradually increase your intake by like 100 each week until you get up to the full amount (daily intake + exercise cals). You'll be less likely to hit a plateau. And if you do, then at least you can adjust your calories lower if needed...unlike right now, you won't be able to do that without eating below the minimum.

Also, those links that LittleSpy posted are GREAT posts, definitely check them out!

If you think your eating enough food and to eat more would be 'too much food' then don't eat anymore.
I tried out and tested the 'eat more loss more' theory and it did not work for me. I gained weight over three months (double the time it's supposed to turn and you start loosing again.), my weight went back up to my original and way beyond. (
I am small frame, short in height and there's no way that the 'normal' rules apply to me. If I eat 1200 cals with no exercise and I gain weight - SIMPLE FACT. Proved throughout my entire life.
You say your still loosing weight and feel ok, then stick at it.
Everyone is different and you have to do what works for you.
I found eating more made me sluggish and lazy and I didn't want to work out and when I did I felt horrible because there was too much food inside my stomach, running- even walking is horrible like than and sit ups are disgusting when full. Makes you not want to work out and it's an effort and unpleasant when you do it.
There's absolutely no way I was ever going to loose weight eating back all my exercise cals. Tested it and it did not work I gained, Big time!! I felt horrible for it too. Now I eat less and eat back some exercise cals and actually enjoy my exercise.
I have much more energy this way and I feel great. And I'm loosing still.
Do what feels right to YOU!! And good luck with your goals

I'm not so sure I agree with having to HAVE to eat your exercise calories (I know this is shocking to some who know me) but hear me out first.
At the beginning, especially for a male who is obese (not sure if you are or not, but judging by your weight loss I'd say that's probably true, or it was before the 18 lbs at least), the maximum deficit of 1000 calories sometimes can be pushed a little bit higher. This is possible for multiple reasons but mainly because how much fat you can burn is tied very closely to how much fat is AVAILABLE to burn. That means the more you have to lose, the larger your deficit can be.

Now This doesn't mean you'll be able to keep this type of deficit up, and as a general rule you should slowly decrease the deficit as you lose the weight, in order to come closer to a more normal eating routine that will allow you to transition from weight loss to maintenance at the end of it all.

One other thing to note, that 1200 calorie thing, that's for the ladies mike, for you, it's supposed to be 1800 calories (generally speaking for men it's 1800 and women it's 1200 as a minimum), why? Well mostly because men have more muscle mass and require more nutrients. But this (like the first concept I stated above) is a very cloudy number, and can be tweaked and played with because in the end, our bodies are all very unique, and what works for me may not work exactly the same for you.

I upped my calories to my goal and ended up gaining weight. I spoke to my doctor who encouraged me to go back to doing what I was before. Everyone's body is different you have to do what works for the individual.

I agree with what others have said about doing what feels good for you and your body also. I just thought I'd share what helped me since I had this mentality at first that if I ate more I couldn't lose weight. But, it was untrue in my case and in many others. As hard and cliche as it sounds, keep listening to your body. Try out different things and see what works, as you go along this journey you'll probably be like the rest of us and keep adjusting to what feels good for you!

BTW, congrats on losing 18 pounds...that is GREAT!!! And cheers to your wife too!! Its so fun to do the journey together...i love working out and eating healthy with my husband!!