Nov 20 (Reuters) - New Zealand's a2 Milk ATM.NZ on Thursday upgraded its full-year earnings forecast, citing stronger-than-expected trading across its core product categories and a weaker New Zealand dollar, but failed to woo investors with shares hitting a near one-month low.

The Auckland-headquartered firm said trading in infant milk formula, or IMF, its top market, was stronger than expected, with English-label IMF revenue growth forecast to outpace China-label IMF growth.

The company, which also sells fresh milk, said movements in actual and forecast currency rates, reflecting a weaker New Zealand dollar, are expected to inflate reported sales and expenses.

Shares of the company pared some of its early losses to trade 0.8% down as of 0001 GMT. The stock fell as much as 4.7%, hitting its lowest level since October 28 in early trade.

"Moving from high single-digit to low double-digit growth is not cosmetic," said Jeremy Sullivan, investment adviser at Hamilton Hindin Greene.

Tom McBride, founder and financial adviser at McBride Wealth, said the stock movement "could be a case of investors expecting higher earnings growth, or it may be a reaction to the increase in capital expenditure."

IMF is the company's top product category, primarily targeting babies and toddlers, and contributed 67% of total sales revenue in fiscal 2025, according to its annual report.

The dairy company now expects low-double-digit revenue growth from continuing operations in fiscal 2026, higher than its previous forecast of high-single-digit growth, and anticipates slightly higher net profit after tax than last year.

Earlier in August, the company announced its fiscal 2025 results and logged a group revenue from continuing operations of NZ$1.76 billion ($984.02 million), while it recorded a 21% jump in its NPAT to NZ$202.9 million.

Trading was also stronger in its other nutritionals and liquid milk product segments, a2 Milk added.

Its nutritionals portfolio comprises non-IMF powdered a2 Milk products, as well as China & other Asia liquid milk products.

The company also expanded the portfolio in the second half of 2025 with the launch of new kids fortified milk powder product, a move that has been received well by the consumers, as per a2's annual report.

($1 = 1.7886 New Zealand dollars)