USDT and USDC both target $1, so the question isn't whether they trade — it's how to move between them without bleeding basis points to gas, slippage, or exchange spread. With Tether sitting near $189.5B in circulation and USDC near $78.1B (DeFiLlama, May 2026), the swap is one of the most common stablecoin operations in crypto, and the cheapest path depends on size, chain, and whether you also need to change networks.
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Below are the four routes that consistently come out cheapest, with real fee math for $100, $1,000, and $10,000 swaps.
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For sub-$1,000 swaps already on an L2 (Base, Arbitrum, Optimism), Uniswap v3's stable pool is cheapest — gas runs sub-cent and slippage on a USDT/USDC 0.01% pool sits under 1 bp. For $10,000+, a Coinbase or Kraken stable-to-stable swap is usually free and avoids slippage entirely. Curve.fi on mainnet is the onchain standard but only beats L2 DEXes when gas drops below $5.
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If your USDT is already on a centralized exchange, or you don't mind a deposit, the cheapest route is almost always a direct stable-to-stable conversion. Coinbase's USDT/USDC conversion is fee-free for retail under the spread on the USDT/USD and USDC/USD books, and Kraken lists USDT/USDC as a direct pair with maker fees starting at 0.25% and falling to 0% above $10M monthly volume (Coinbase fee schedule; Kraken fee schedule, 2026).
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Practical fee math:

When to use: Larger sizes ($5,000+), tight depeg moments where DEX slippage widens, or when you also need to withdraw fiat. The catch is deposit/withdrawal cost — if your USDT is on TRC20 and you need USDC on Base, you're paying network fees on both legs. For TRC20 specifics, see TRC20 vs ERC20: Network Differences.
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Curve.fi's 3pool (DAI/USDC/USDT) is the reference onchain venue for stable swaps. Its StableSwap invariant compresses slippage on near-pegged assets, so a $10,000 USDT→USDC swap typically clears at under 1 basis point of slippage when the pool is balanced (Curve.fi docs, 3pool). The 0.04% pool fee is split between LPs and the DAO.
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Cost on a typical day with mainnet base fee around 8 gwei:

When to use: Your USDT and target USDC both live on Ethereum mainnet, the size is $5,000+, and you don't want CEX exposure. Aggregators like 1inch and CoW Swap will route through 3pool automatically and sometimes split across Curve + Uniswap for better fills on six-figure trades.
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On Base, Arbitrum, and Optimism, Uniswap v3 runs USDT/USDC pools at 0.01% and 0.05% fee tiers. With L2 gas typically pricing a swap at $0.005–$0.05 after EIP-4844 blob compression, this is the cheapest onchain route for retail-sized swaps (Uniswap v3 docs; L2Fees.info, 2026).
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Fee math on Base or Arbitrum at typical 2026 gas:

When to use: You're already on an L2 and your size is under $25,000. For larger swaps, check pool depth on the specific tier — Base USDT liquidity is thinner than Arbitrum, so a $50,000 trade may slip 5–10 bp.
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If you're swapping USDT to USDC and changing chains in the same step — say, USDT on Ethereum to USDC on Base — a cross-chain aggregator quotes a single transaction that bundles the swap with the bridge. LI.FI, Squid, and Across route through their own liquidity plus DEX legs on each side (LI.FI docs, 2026).
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Typical all-in cost:

When to use: Origin and destination chains differ. Don't use a cross-chain aggregator if you're staying on the same chain — you'll pay an unnecessary spread.
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The cheapest route shifts slightly per chain because liquidity depth and gas cost vary.
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Base: Uniswap v3 USDT/USDC 0.01% pool is the default. Aerodrome runs a competing stable pool — check both via 1inch or Matcha. Gas under $0.05 per swap.
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Arbitrum: Deepest L2 stable liquidity. Uniswap v3 + Curve's Arbitrum 2pool both work; aggregators usually split the order. Gas ~$0.02.
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Polygon: QuickSwap and Uniswap v3 both list USDT/USDC. Polygon PoS gas is cheap (~$0.01), but watch which USDT/USDC variant you hold — bridged vs native. The 2024–25 transition to native USDC on Polygon left some pools fragmented across USDC.e and native USDC.
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Solana: Jupiter aggregates across Orca, Raydium, and Meteora's USDT/USDC pools. Fees clear in 1–3 cents including the SOL priority fee. Solana's USDT depth is smaller than its USDC depth (USDT supply on Solana is roughly a tenth of USDC's), so very large swaps may slip more than on Ethereum L2s.
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Yes — meaningfully. Slippage on a Uniswap v3 0.01% pool is near zero for retail, but at $100,000+ even the deepest pools start showing 5–20 bp of price impact. A CEX direct swap or limit order avoids slippage by paying maker rebates instead of taker fees, so for institutional-size rebalances the CEX route quietly wins. Conversely, for $50 swaps the L2 DEX route is the only one where fees stay under 10 bp of the trade.
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On well-balanced pools, USDT/USDC slippage tracks the depeg risk of either token. During the March 2023 USDC depeg, Curve 3pool slippage on a $10,000 swap briefly widened to over 100 bp because the pool went 70% USDC. In calm markets, expect:

Always set a slippage tolerance — 0.1% is reasonable for stable swaps in normal conditions, 0.5% if a depeg is brewing.
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Gas figures use 2026 mainnet and L2 averages from L2Fees.info. Pool fee tiers reference Uniswap v3 official documentation and Curve.fi pool pages. CEX fee schedules pulled from Coinbase Advanced and Kraken fee pages, May 2026. Stablecoin supply totals from DeFiLlama's stablecoin dashboard. Cross-chain fee ranges from LI.FI's documentation and Across Protocol relayer fee disclosures. No swap fees were calculated for trades over $1M; large block trades typically require OTC quotes outside the routes above.
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