Voice AI Cost Calculator: STT + LLM + TTS

A voice AI call costs the sum of speech-to-text (STT), LLM, and text-to-speech (TTS) for that call. ByteCosts calculates STT + LLM + TTS cost per call, then multiplies it by monthly call volume to show the monthly voice-agent run rate. STT uses call minutes and your per-minute assumption; LLM cost uses turns per call, input and output tokens, selected model rates, and cache settings; TTS uses turns and the selected model's billed seconds or characters. Use the per-call result as the cost floor before adding telephony, escalation, support, and margin.

Example scenario

Suppose a voice agent handles four-minute calls with seven LLM and TTS turns per call. Enter the daily call volume, STT rate, token shape, LLM model, and TTS model. The calculator prices each layer separately, adds them into cost per call, and scales that result to a 30-day monthly call volume. Compare a normal month with a heavier-volume case before using the result in a customer or support-margin model.

What the inputs mean

• Call volume: calls per day, converted to monthly calls with a 30-day month.
• STT workload: minutes per call and your speech-to-text rate per minute.
• LLM workload: turns per call, input and output tokens per turn, selected model, and cache assumptions.
• TTS workload: selected speech model plus its billed seconds or characters per turn.

What the result means

You get the STT, LLM, and TTS monthly subtotals, their combined monthly cost, and cost per call at the entered monthly volume. Carry cost per call into Scenario Studio for the wider workload or into Per-User Gross Margin to test whether the product price covers voice AI COGS.

Assumptions

• Monthly call volume uses calls per day times 30, matching the live calculator.
• STT is an editable per-minute assumption rather than a live provider quote.
• LLM rates and supported cache behavior come from the committed source-backed model index.
• TTS cost follows the selected model’s committed billing unit, including seconds or characters where applicable.
• Telephony, human escalation, storage, taxes, negotiated rates, and support overhead are outside the displayed total.

Where the prices come from

STT is an editable per-minute assumption. LLM input, output, and supported cache rates come from the committed ByteCosts provider pricing index. TTS uses the selected model’s committed fal.ai billing unit and price. The page reads those stored records and never calls a provider or refreshes prices from the browser.

Formula and methodology

Monthly calls = calls per day × 30. STT cost per call = minutes per call × STT rate per minute. LLM cost per call = turns per call × cache-adjusted token cost per turn, using selected model input and output rates. TTS cost per call = turns per call × the selected TTS model's cost for its billing unit, such as seconds or characters. Monthly cost = monthly calls × (STT cost per call + LLM cost per call + TTS cost per call). Per-call cost is monthly cost divided by monthly calls. Standard arithmetic; no model internals.

Interpretation guide

• Compare alternatives with the same workload assumptions.
• Stress-test output-heavy, retry-heavy, cache-miss, and power-user cases before committing budget.
• Verify source links and production logs before using the estimate for billing decisions.

Limitations before production billing decisions

Treat ByteCosts calculations as planning estimates, not final billing totals. Real invoices can differ because token mix, retry rate, cache hit rate, rate limits, taxes, gateway fees, regional pricing, and negotiated discounts change the effective cost.

Verify the provider source before production billing decisions, then compare the estimate with your own logs or invoice once production traffic is live.

Voice AI Cost Calculator: STT + LLM + TTS. ByteCosts. https://bytecosts.com/tools/voice-ai-cost/

Sources

• fal.ai media pricing - Verify source-backed TTS billing units and rates
• Per-User Gross Margin - Convert cost per call into product margin
• ByteCosts methodology
• ByteCosts provider pricing index