The Northern Star Resources Ltd (ASX: NST) share price is falling hard today.

Shares in the S&P/ASX 200 Index (ASX: XJO) gold stock closed on Friday trading for $18.39. In morning trade on Monday, shares are changing hands for $17.19 apiece, down 6.5%.

For some context, the ASX 200 is just about flat at this same time, while the S&P/ASX All Ordinaries Gold Index (ASX: XGD) is down 1.8%

Here's what's catching ASX investor interest today.

Northern Star share price tumbles on update

The Northern Star share price is catching headwinds following the release of an operational update and revised full fiscal year 2025 (FY 2025) guidance.

The miner reported selling 444,000 ounces of gold during the June quarter. That sees the total gold sold in FY 2025 to 1.634 million ounces. This falls within Northern Star's revised full-year guidance range of 1.630 to 1.660 million ounces of gold.

Management also expects that the all-in sustaining cost (AISC) in FY 2025 will be within the revised cost guidance range of AU$2,100 to AU$2,200 per ounce.

The Kalgoorlie Production Centre underperformed the revised guidance range, with total gold sold of 832,000 ounces, compared to guidance of 850,000 to 860,000 ounces.

But with Pogi producing 283,000 ounces, at the top end of guidance, and the production centre selling 518,00 ounces of gold, at the midpoint of revised guidance, the ASX 200 miner remains on its full-year production target.

What's next?

Looking to what could impact the Northern Star share price in FY 2026 and beyond, the miner said it continues to advance major growth projects to achieve its goal of being "a long-life, high margin, returns focused global gold producer at the bottom half of the global cost curve".

According to Northern Star, "The KCGM Mill Expansion is one of the key enablers to achieving this goal and with mill commissioning on track for early FY27, ancillary projects are required in readiness."

Management provided FY 2026 guidance of 1.700 to 1.800 million ounces of gold sold. KCGM is forecast to deliver 550,000 to 600,000 ounces of gold.

Perhaps weighing on the share price today, September is expected to be the softest quarter for the miner overall amid planned major shutdowns across all three of its production centres. Production is expected to pick up in the latter quarters of FY 2026.

And on the cost front, management forecasts FY 2026 AISC to be in the range of AU$2,300 to AU$2,700 per ounce. While that's expected to improve throughout the year, AISC is forecast to be significantly higher than in FY 2025.

Northern Star is scheduled to release its June quarterly results on 24 July.

With today's intraday fall factored in, the Northern Star share price remains up 34.2% over 12 months.