Part of a series on building Balance, a portfolio rebalancing app for BR/US/Crypto
investors, as a solo developer. Code in this article is simplified from the real service.
Every investor who makes recurring contributions hits the same wall:
"I have $1,000 to invest this month. What do I buy so my portfolio stays close to my target allocation?"
The textbook answer — "sell what's overweight, buy what's underweight" — has a cost: taxes, brokerage fees, and the emotional discipline to sell things that are going up. There's a gentler approach that most people never formalize: rebalance using only the new deposit.
