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Primer Tm Calculator

Calculate primer Tm and suggested Ta for up to 200 pairs—QC flags, no upload. Built-in AI agent assistant support.

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Key facts

Key facts about Primer Tm Calculator
FactValue
InputsForward and reverse sequences (single) or CSV/TSV with name, fwd, rev (batch); polymerase preset or custom Na⁺, Mg²⁺, dNTPs
Polymerase presetsQ5 (NEB), Phusion, Taq (standard), KAPA HiFi, Custom buffer
AdditivesDMSO % (0–10); Formamide % (0–20); betaine not supported (must be 0)
OutputsTm forward/reverse, ΔTm, suggested Ta, GC%, hairpin ΔG, dimer ΔG, Go/Flag/Fail status
Batch limitUp to 200 primer pairs per run
Method comparisonWallace, %GC rule, SantaLucia raw/corrected, Breslauer (single mode)
Runs in browserYes — no install; sequences not uploaded
Account requiredNo
HistoryLast 20 runs stored locally in browser

What it does

Cross-tool Tm disagreement and one-at-a-time entry waste time when you need Ta for a full primer panel before ordering oligos or setting a gradient PCR. The Primer Tm Calculator returns Tm for each primer, ΔTm between partners, a suggested annealing temperature (Ta) matched to your polymerase buffer, and pass/fail QC for hairpins and primer dimers—in one browser session with no sequence upload.

Enter forward and reverse sequences in single mode, or paste or upload a batch file with name, fwd, and rev columns (up to 200 pairs). Select Polymerase—Q5 (NEB), Phusion, Taq (standard), KAPA HiFi, or Custom buffer with editable Na⁺, Mg²⁺, and dNTPs (mM, each). Set DMSO % (0–10) or Formamide % (0–20) when your mix includes co-solvents; open Show advanced to adjust oligo concentration (nM). Invalid non-ACGT bases highlight as you type.

Click Calculate to see Tm forward, Tm reverse, ΔTm, Suggested Ta, GC% badges, hairpin and dimer ΔG, and a Go/Flag/Fail chip. Expand Method comparison to see Wallace, %GC, SantaLucia, and Breslauer values beside the salt-corrected result used for Ta. Batch runs show a sortable table; use Export CSV, Copy table or Copy summary, or PDF / Print. Reload past runs from the History tab (last 20, stored locally).

Why researchers use it

  • Process up to 200 primer pairs in one batch run
  • Keep proprietary sequences on your machine only
  • Adjust Tm for DMSO and formamide in your mix
  • Catch unbalanced Tm and dimer issues before PCR
  • Match Ta to Q5, Phusion, Taq, or KAPA buffer presets
  • Compare why vendor calculators disagree on Tm

Best for

  • Multiplex and panel PCR primer design
  • NGS amplicon primer QC before ordering
  • GC-rich reactions with DMSO or formamide in the mix
  • Gradient PCR planning for new primer sets
  • Core facility review of submitted primer orders
  • Checking ΔTm balance across a primer library

When to use this vs alternatives

Choose this tool when batch Tm, suggested Ta, hairpin/dimer flags, and additive corrections must live in one private browser workflow. Use the PCR Master Mix Calculator after Ta is set to plan reaction volumes, overage, and a printable bench sheet. NEB Tm Calculator still fits labs standardized on NEB enzymes who accept server-side sequence entry. IDT OligoAnalyzer suits deep single-oligo QC when you need extinction coefficient detail and can enter primers one at a time.

What makes it different

Most free tools offer either batch Tm or structure checks—not both—with vendor-specific buffers and no co-solvent correction. NEB Tm Calculator is trusted for NEB enzymes but sends sequences to NEB servers and skips dimer QC. IDT OligoAnalyzer handles hairpins and dimers but one primer at a time, with no DMSO or formamide correction.

This browser primer Tm calculator combines batch output, Q5/Phusion/Taq/KAPA/custom buffer presets, DMSO and formamide adjustment, hairpin and dimer flags, and a method comparison panel—without uploading sequences. Researchers switch when they loop Excel through NEB for Tm and IDT for dimers, or when co-solvents in the mix make vendor Ta suggestions too high. Results export to CSV or print for lab notebooks.

How to get started

  1. Open the workspace and stay on the Calculator tab.
  2. Choose single or batch; enter sequences or paste CSV with name, fwd, rev columns (Download sample CSV if needed).
  3. Select Polymerase; set DMSO % and Formamide % if used; expand Custom buffer or Show advanced when needed.
  4. Click Calculate.
  5. Review Tm forward, Tm reverse, ΔTm, Suggested Ta, and Go/Flag/Fail status; expand Method comparison if values differ from another tool.
  6. Click Export CSV, Copy table or Copy summary, or PDF / Print; reload a past run from History if needed.

Frequently asked questions

Why do Tm calculators give different values?
Different tools use different thermodynamic parameter sets (SantaLucia 1998 vs Breslauer 1986), salt correction models, and oligo concentration defaults—so the same primer can differ by 3–10°C. Mg²⁺ and dNTP chelation change effective monovalent salt; a calculator set to Na⁺ only will read higher than one that includes your PCR buffer. This tool uses SantaLucia 1998 with Owczarzy 2008 salt correction and shows Wallace, %GC, SantaLucia raw, and Breslauer values in Method comparison so you can see where divergence comes from. Match polymerase and additive settings to your actual reaction.
How do I calculate annealing temperature from primer Tm?
Annealing temperature (Ta) is the PCR cycle temperature where primers bind; it is derived from the lower of the two primer Tm values. For Taq (standard) and Custom buffer, suggested Ta is lower Tm minus 5°C. For Q5 (NEB), Phusion, and KAPA HiFi, suggested Ta is lower Tm plus 3°C when both primers exceed 20 nt; otherwise lower Tm. DMSO (−0.675°C per 1%) and formamide (−0.6°C per 1%) reduce Tm before Ta is computed. Confirm with a gradient PCR when templates are difficult or primers are near design limits.
What ΔTm between primers is acceptable?
Primer pairs work best when forward and reverse Tm values are close—typically within 5°C, ideally within 2–3°C. This tool flags pairs with ΔTm above 5°C (Flag) and above 10°C (Fail). Large ΔTm means one primer may anneal poorly at the chosen Ta, increasing non-specific products or drop-out. Redesign the outlier primer or accept a wider gradient range. Batch mode highlights failing rows so you can sort by ΔTm before ordering oligos.
Can I batch-process many primer pairs?
Yes. Switch to batch mode and paste or upload a CSV/TSV with name, fwd, and rev columns (header optional). The limit is 200 pairs per run; extra rows are truncated with a notice. Results appear in a sortable table with Tm F, Tm R, ΔTm, GC%, Ta, Status, Hairpin ΔG, and Dimer ΔG. Click Export CSV for a spreadsheet with QC annotations, or Copy table for TSV. Polymerase and additive settings apply to the entire batch.
Does DMSO or formamide change primer Tm?
Yes. DMSO destabilizes duplexes; this tool applies −0.675°C per 1% DMSO. Formamide lowers Tm about −0.6°C per 1% (v/v). Enter values in DMSO % (slider 0–10) and Formamide % (0–20) before calculating. Warnings appear above 10% for either additive because high co-solvent can inhibit polymerase. Betaine Tm correction is not implemented—leave Betaine (M) at 0.
What do hairpin and dimer ΔG flags mean?
Hairpin ΔG estimates intramolecular folding in a single primer; dimer ΔG estimates hetero-dimer formation between forward and reverse partners—both computed with SantaLucia nearest-neighbor thermodynamics at 37°C. Hairpin ΔG below −2 kcal/mol triggers Flag; dimer ΔG below −6 kcal/mol triggers Fail. Strong dimers compete with template annealing and often cause smears or no product. A Go status does not replace empirical PCR—it means Tm balance, GC%, and structure scores passed default thresholds for the pair.

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