Do I need to pay/report anything if I rebalance my portfolio? (Not taking any money to my checking acc, just selling and buying inside Fidelity)
If you sell in a brokerage account (not IRA), then at the end of the year, Fidelity will send you 1099 forms to report your sales’ capital gains to file with your tax return.
As @Mindi said, if you sell any funds in a taxable account, then you’ll report those gains (or losses) on your taxes for that year. That may or may not be a big deal depending on how big those amounts are and the rest of your tax situation.
IN GENERAL, rebalancing isn’t actually all that big of a deal. Some experts basically think you never need to do it, or even that rebalancing can actually hurt your long term growth during your wealth accumulation years (because you’re more often selling high producing assets for lower ones).
You can always just rebalance by buying what you’re low on instead of selling. So for example, if your target asset allocation is 60% US, 30% international and 10% bonds, but currently you have only 55% US, 35% international and 10% bonds. Next time you buy more, just buy US and not international to get closer to your target allocation. That way you’re not selling anything and triggering a taxable event