PCR Annealing Temperature Calculator (Ta = Tm − 5°C)

PCR Annealing Temperature Calculator (Ta = Tm − 5°C) | Online Free Tool | Elysia Tools

Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category: Education
Input types: select, number
Output type: json
Sample coverage: 4
API ready: Yes

Overview

The PCR Annealing Temperature Calculator estimates Ta from forward and reverse primer Tm values using either the simple lower-Tm-minus-5°C rule or the Rychlik 1990 formula, which also uses product Tm. It returns the selected Ta, a ±3°C gradient range, and a warning when primer Tm values differ too much. Use the results for lab planning only.

When to use

Choose an initial PCR annealing temperature from a primer pair's forward and reverse Tm values.
Plan a gradient PCR using the calculated Ta and its ±3°C testing window.
Compare the simple Tm − 5°C rule with the Rychlik 1990 formula when product Tm is available.

How it works

1Enter the forward primer Tm, reverse primer Tm, and product Tm.
2Select the Simple rule or Rychlik formula calculation method.
3The simple rule subtracts 5°C from the lower primer Tm; the Rychlik formula calculates 0.3 × primer Tm + 0.7 × product Tm − 14.9.
4The calculator reports the selected Ta, a range extending 3°C below and above it, and a primer-Tm mismatch warning when applicable.

Use cases

Set an initial annealing temperature for a new primer pair.
Define a gradient PCR range when optimizing specificity and amplification.
Cross-check a simple Ta estimate against the Rychlik formula for a known product Tm.

Examples

1. Standard primer pair using the simple rule

PCR researcher

Background

A primer pair has forward Tm 62°C and reverse Tm 60°C, with an estimated product Tm of 85°C.

Problem

Choose an initial annealing temperature and a practical gradient range.

How to use

Select Simple rule, enter forwardTm 62, reverseTm 60, productTm 85, and set Decimal Places to 1.

{"rule":"simple","forwardTm":62,"reverseTm":60,"productTm":85,"decimalPlaces":1}

Outcome

The calculator returns Ta = 55°C with a 52–58°C gradient range. The 2°C primer-Tm difference does not trigger a mismatch warning, and the Rychlik cross-check is 62.6°C.

2. Rychlik formula for a higher-temperature comparison

Molecular biology student

Background

The same primer pair has Tm values of 62°C and 60°C, and the product Tm is 85°C.

Problem

Estimate Ta with the Rychlik 1990 formula and compare it with the simple rule.

How to use

Select Rychlik formula, enter forwardTm 62, reverseTm 60, productTm 85, and set Decimal Places to 1.

FAQ

Which primer Tm does the simple rule use?

It uses the lower Tm of the forward and reverse primers, then subtracts 5°C.

What is the Rychlik formula?

It is Ta = 0.3 × primer Tm + 0.7 × product Tm − 14.9.

What does the gradient range mean?

It is a suggested testing window extending 3°C below and above the calculated Ta.

Why is a primer-Tm mismatch warning shown?

The warning indicates that the forward and reverse primer Tm values differ beyond the recommended range.

Is this calculator a complete PCR protocol?

No. It provides temperature calculations for lab planning and does not replace assay-specific optimization.

{"rule":"rychlik","forwardTm":62,"reverseTm":60,"productTm":85,"decimalPlaces":1}

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Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Overview

When to use

How it works

Use cases

Examples

1. Standard primer pair using the simple rule

2. Rychlik formula for a higher-temperature comparison

FAQ

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