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Thailand’s SET Index closed at 1,539.12 on 14 May 2026, up 1.44% on the day after positive US-China summit news. That’s a relief rally from the 1,489 low on 11 May. Over the past month, SET50 has climbed about 1.1%. Year-on-year, SET50 is up 27.6% — a respectable number that obscures how choppy 2026 has been.
Meanwhile, the S&P 500 hit a new all-time high in April and has been consolidating since. Year-to-date through mid-May, the S&P is up roughly 4%. Year-on-year it’s up around 14%. The two markets are sending different signals, and Thai investors trying to decide where to overweight need to weigh several things.
The fundamental gap
Thai GDP grew 2.4% last year, well below regional peers like Vietnam (6%+), Philippines (5.5%), Indonesia (5%). The Finance Ministry has warned policy space is limited, with public debt at 66% of GDP, close to the 70% ceiling. The BOT is at a 1% policy rate, also constrained.
The US grew about 2.5% last year despite higher rates. Corporate earnings remain strong, with Q1 2026 results broadly beating expectations. The Iran war is a clear drag — April CPI at 3.8% reflects oil-driven inflation — but the US economy is structurally more resilient than Thailand’s.
The valuation gap
The SET trades at a forward P/E of around 14x — cheap by global standards. The S&P 500 trades around 20x forward. On simple valuation, Thailand looks like better value. But valuation gaps usually exist for reasons. Thailand’s lower growth, smaller market cap, thinner liquidity, and political uncertainty all justify some discount.
What’s interesting in May 2026: the SET’s discount has widened beyond historical norms. Foreign outflows have persisted through April-May. Some analysts argue the value is now compelling enough that mean reversion is more likely than further widening. Others note that Thai markets have looked cheap for years without rerating.
The currency overlay
This is where Thai investors face a choice US-based investors don’t. USD/THB has moved from below 32 to 32.62, weakening THB by about 2% recently. If you invested in S&P 500 a year ago through a USD-denominated mutual fund and the S&P is up 14% in USD terms, your THB return is closer to 16% once you account for the currency move.
Conversely, if you invested in SET stocks through a THB account, the 27.6% year-on-year SET50 return is your full return — no currency benefit, no currency drag.
For a 5-year horizon, the currency overlay matters less than for a 1-year horizon. Currencies mean-revert over long periods. But for the next 12-24 months, with Thailand structurally trapped at low rates, currency drag is more likely than currency tailwind for THB holders. That tilts the math toward USD exposure for shorter horizons.
What’s driving the May 2026 SET rally
Several supportive factors. Q1 2026 corporate earnings have generally beaten expectations, particularly in petrochemicals (SCC, PTTGC, IVL benefiting from product spreads), ICT (TRUE, AIS), and selected financials. Moody’s upgraded Thailand’s outlook recently. The US-China summit drove foreign fund inflows. The Bhumjaithai-led government’s pro-business orientation is helping sentiment.
Risk factors: persistent Middle East tensions, Constitutional Court consideration of the THB 400 billion loan decree, and the lack of dominant Thai tech names that mirror the US tech-led rally have all weighed at various points.
Allocation framework for Thai investors
For most Thai retail investors with moderate risk tolerance, a diversified split makes more sense than betting on one market. A reasonable framework: 40-50% domestic equities (SET via direct or fund), 30-40% US equities (via foreign funds or direct), 10-15% other Asian markets (Japan, Korea, regional ETFs), 10-20% bonds and cash.
If you’re tax-optimizing, Thai ESGX and Thai ESG funds give domestic equity exposure with tax deductions of up to ฿300,000 per year through 2026. RMF funds give US equity exposure with the same tax-deduction window if you invest through Thai-domiciled US-equity RMFs.
The short answer
For a 1-3 year horizon: tilt toward US, given the structural advantages and currency tailwind. For a 5-10 year horizon: tilt toward Thai equities, given the valuation discount. For most diversified portfolios: hold both at meaningful weights and rebalance annually.
The mistake to avoid: chasing whichever market is performing best at the moment. SET ran hard before March 2026 and then gave back gains. S&P 500 hit a high in April and has consolidated. Performance chasing in either direction generally underperforms a disciplined allocation.
