AI Transcription (Speech-to-Text) API Cost Calculator

The calculator takes a single audio duration, multiplies it by the number of files in your batch, and prices that volume against every provider's published pay-as-you-go rate. All rates are stored as a single source value — per minute or per hour exactly as the vendor lists it — and converted to a common per-minute basis for the comparison.

1. Normalise the duration. Hours are multiplied by 60. Your length is treated as the size of one file; the file count then scales the total: total minutes = length × 60 (if hours) × files.
2. Apply each vendor's billing granularity. Whisper rounds to the nearest second; Deepgram, AssemblyAI and Azure bill per second — for all four, billed minutes equal the entered minutes. Google rounds each request up to the next 15-second increment: billed = ceil(minutes ÷ 0.25) × 0.25 per file, which adds a premium when you send many short clips.
3. Subtract the free tier.When you pick “Per month”, Google's first 60 audio minutes each month are removed before pricing. One-off jobs do not get a monthly free allowance.
4. Price it. cost = billed minutes × rate per minute. Per-hour list prices (AssemblyAI Best and Nano, Azure) are divided by 60 to get the per-minute rate; that derivation is cross-checked in the data module so the per-hour and per-minute views always agree.
5. Convert and project. LKR is cost × USD→LKR using the editable, CBSL-sourced rate. For monthly jobs the annual figure is simply the monthly cost × 12. The effective cost-per-hour column lets you eyeball providers regardless of clip length.

Every rate links to the vendor's own pricing page and carries a last-verified date. The comparison covers pre-recorded, standard tiers only — streaming, real-time, and speaker-diarization surcharges are out of scope so the rows stay apples-to-apples, and enterprise volume discounts are not modelled.

• OpenAI — API pricing (Whisper, whisper-1 per-minute rate)
• Deepgram — pricing (Nova pre-recorded pay-as-you-go)
• AssemblyAI — pricing (Best and Nano per-hour rates)
• Google Cloud — Speech-to-Text pricing (15-second increments, 60 free min/month)
• Microsoft Azure — AI Speech pricing (standard speech-to-text per hour)
• Central Bank of Sri Lanka — daily indicative USD/LKR rate

These rates were last cross-checked against each vendor's pricing page on 2026-06-05. API pricing changes frequently — confirm against the linked source before committing to a provider. The USD→LKR field is editable so you can match the rate your bank gives you.