Better to overestimate or underestimate?

So I know it's impossible to accurately measure food without a scale, but since my family already think I'm being too obsessive about my weight-loss there's no way I can get one without them staging an intervention - seriously, when I began to cut down on carbs they gave me an hour-long lecture about it and made sure I ate a plate full of rice right after. Note that I didn't cut them out entirely, I still have rice and pasta and bread and even cake and fairly often too, but in smaller portions than they're used to. In lieu of a scale, I've been trying to roughly estimate what I eat based on internet consensus (3oz of meat=a deck of cards, for instance) but I know that's probably inaccurate so I tend to overestimate when I log.

I'm 19, 5'4 and 68 kilos/about 150 pounds. My calorie goal is 1600 a day, sometimes I go over and sometimes under but I aim to average it out over the week. My BMR is 1500 and my TDEE is 2340 since I'm doing P90X. TDEE-20% brings me to about 1870 calories but I don't want to aim for 1800 when I might be eating that much already and not know. My weight loss has been pretty steady thus far, though I rarely weigh myself but I shrink out of my clothes really fast. The thing is, P90X is kicking my *kitten* and I'm concerned I might not be giving my body enough fuel to recuperate.

I think I'm overestimating what I log, but I might not be and without a scale I guess I'll never know. Question is, should I try upping my calories and hope for the best, or stay where I am?